CODING
Public Class Form1
   
    Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)
      
    End Sub

    Private Sub TextBox2_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox2.TextChanged
        If CheckBox1.Checked Then

            TextBox2.Text = "10%"
        End If
        If CheckBox1.Checked And CheckBox2.Checked Then
            TextBox2.Text = "15%"

        End If
        If CheckBox1.Checked And CheckBox3.Checked Then
            TextBox2.Text = "15%"

        End If
        If CheckBox2.Checked Then
            TextBox2.Text = "5%"
        End If
        If CheckBox3.Checked Then
            TextBox2.Text = "5%"
        End If
        If CheckBox2.Checked And CheckBox3.Checked Then
            TextBox2.Text = "10%"
        End If



    End Sub

    Private Sub CheckBox1_CheckedChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CheckBox1.CheckedChanged

    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        TextBox3.Text = TextBox5.Text * TextBox1.Text



    End Sub

    Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
        If TextBox2.Text = "10%" Then
            TextBox4.Text = TextBox3.Text - (TextBox3.Text * 0.1)

        End If
        If TextBox2.Text = "5%" Then
            TextBox4.Text = TextBox3.Text - (TextBox3.Text * 0.05)

        End If
        If TextBox2.Text = "15%" Then
            TextBox4.Text = TextBox3.Text - (TextBox3.Text * 0.15)
        End If
        If TextBox2.Text = "20%" Then
            TextBox4.Text = TextBox3.Text - (TextBox3.Text * 0.2)
        End If
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        TextBox1.Text = " "
        TextBox2.Text = " "
        TextBox3.Text = " "
        TextBox4.Text = " "
        TextBox5.Text = " "
        ComboBox1.Text = " "
        ComboBox2.Text = " "
       
    End Sub
End Class

Codingan Form1
Public Class Form1

    Private Sub Label2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Label2.Click

    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

    End Sub

    Private Sub TextBox4_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox4.TextChanged

    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        TextBox2.Text = ""
        TextBox3.Text = ""
        TextBox4.Text = ""
        TextBox5.Text = ""
        TextBox6.Text = ""


    End Sub

    Private Sub Label8_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Label8.Click

    End Sub

    Private Sub TextBox3_LostFocus(ByVal sender As Object, ByVal e As System.EventArgs) Handles TextBox3.LostFocus
        TextBox3.Text = TextBox2.Text * TextBox4.Text
    End Sub

    Private Sub TextBox3_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox3.TextChanged


    End Sub

    Private Sub Label5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Label5.Click

    End Sub

    Private Sub TextBox10_LostFocus(ByVal sender As Object, ByVal e As System.EventArgs) Handles TextBox10.LostFocus
        TextBox10.Text = TextBox9.Text * TextBox8.Text
    End Sub

    Private Sub TextBox10_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox10.TextChanged


    End Sub

    Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
        TextBox8.Text = ""
        TextBox9.Text = ""
        TextBox10.Text = ""
        TextBox11.Text = ""
        TextBox12.Text = ""

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        TextBox6.Text = TextBox3.Text * 1 + TextBox5.Text * 1

    End Sub

    Private Sub TextBox5_LostFocus(ByVal sender As Object, ByVal e As System.EventArgs) Handles TextBox5.LostFocus
        If TextBox3.Text > 70000000 Then
            TextBox5.Text = TextBox3.Text * 0.1
        End If

    End Sub

    Private Sub TextBox5_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox5.TextChanged
       



    End Sub

    Private Sub TextBox11_LostFocus(ByVal sender As Object, ByVal e As System.EventArgs) Handles TextBox11.LostFocus
        If TextBox10.Text > 12000000 Then
            TextBox11.Text = TextBox10.Text * 0.1

        End If
    End Sub

    Private Sub TextBox11_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox11.TextChanged

    End Sub

    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        TextBox12.Text = TextBox10.Text * 1 + TextBox11.Text * 1

    End Sub

    Private Sub TextBox13_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox13.TextChanged

    End Sub

    Private Sub Button5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button5.Click
        TextBox13.Text = TextBox6.Text * 1 + TextBox12.Text * 1

    End Sub

    Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)

    End Sub

    Private Sub Button6_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button6.Click
        End

    End Sub
End Class