Public Class interest
    ' calculate compound interest factor, given rate% and number of periods
    Private Function CompoundInterest(ByVal rate As Double, ByVal number As Double) As Double
        Return (1 + rate / 100) ^ number
    End Function
    ' calculate monthly repayment given capital, rate% per month, and number of months
    Private Function MonthlyRepayment(ByVal capital As Double, ByVal rate As Double, ByVal number As Double) As Double
        Return capital * (rate / 100) / (1 - 1 / CompoundInterest(rate, number))
    End Function
    ' perform calculation and display results
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim capital As Double = TextBox1.Text
        Dim rate As Double = TextBox2.Text / 12
        Dim period As Double = TextBox3.Text * 12
        TextBox4.Text = MonthlyRepayment(capital, rate, period).ToString("F02")
        TextBox5.Text = CInt(period * MonthlyRepayment(capital, rate, period))
    End Sub
End Class