problem

[CSTHOM1]

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
' Variables
Dim PV, FV, r, n As Decimal

' Input
FV = TextBox1.Text
r = TextBox2.Text / 1200
n = TextBox3.Text

' Process
PV = FV * (r / 1 - (1 + r) ^ -12 * n)

' Output 
TextBox4.Text = PV.ToString("C2"