Simple VB Calculation

I’m new to VB and I’m completely stumped on a calculation assignment for my class. I’ve built a form with 10 checkboxes, and each have a different dollar amount assigned to them (prices for veterinary services). I can’t figure out what code I needto assign to the command button to display the sum of only the checked boxes. How do I single out only the selected boxes to be calculated so that their sum will be displayed? Thanks for any help!