List To Update Every Time And Show The Values Each Time To Which The Previous Value Is Added To The New Calculation?

The idea with this form is to add the futures which is calculated when the button is pushed but I need the list to update every time and show the values each time to which the previous value is added to the new calculation, e.g. of what it should look like in listbox:

Year 1: $1,290.93
Year 2: $2,724.32
Year 3: $4,350.76
etc....

I have been working on this a while and I am at a standstill, I was given a function to clear the form everytime it calculates but I don't know how to implement it, I am new to VB. Here is what I have so far:

Public Class frmFutureValue
Private Sub btnCalculate_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnCalculate.Click

[code]....