Sub procedure and a Function procedure

I have to get a value in $.

I have 2 radio buttons:
Residential Customers
Business Customers

I have 2 List boxes:
Premium Channels
Connections

I also have a total Text Box and a calculate button



My goal is to get a cost given the information from the user. the list boxes will have preassigned numbers in them


Variables:
The residential Customers have to pay a $4.50 Processing fee, a Basic service fee of $30 and 5$ for ever Premium Chanel they buy.

The Business Customers have to pay a processing fee of $16.50, a basic service fee of $80 for the first 10 connections (4$ for any connection after that) and 50$ per Premium Chanel (no limit)


Can Anyone HELP?! I am totally stuck!!

The project calls for a Sub and function procedure.

What I am working on:

Assign objects to List Boxes in the MainForm

premiumListBox.Items.Add("1")
premiumListBox.Items.Add("2")
premiumListBox.Items.Add("3")
premiumListBox.Items.Add("4")
premiumListBox.Items.Add("5")
premiumListBox.Items.Add("6")
premiumListBox.Items.Add("7")

connectionsListBox.Items.Add("1")
connectionsListBox.Items.Add("2")
connectionsListBox.Items.Add("3")
connectionsListBox.Items.Add("4")
connectionsListBox.Items.Add("5")
connectionsListBox.Items.Add("6")

Then Assign Variables

Dim premium As Double

Dim connections As Decimal
Dim total As Integer
Dim businessradiobutton As Decimal
Dim residentialradiobutton As Decimal


Integer.TryParse(totalTextBox.Text, total)
Double.TryParse(premiumListBox.SelectedItem.ToString, premium)
Double.TryParse(connectionsListBox.SelectedItem.ToString, connections)

The Radio Buttons will have a value.

Residential is $4.5 for processing fee and $30 for Basic Service
so..... residentialradiobutton = $34.5

as businessradiobutton = $80 for 10 connections and the $4 for each additional connection
so...... businessradiobutton =
if businessradiobutton >= 10 then
businessradiobutton = 80 else
businessradiobutton = ?????