Check with your printer's manual. This will define how much of a margin that the printer will not print to.
Ideally, you could create a document in InDesign that is 7" wide by 10" tall. This would allow you to place 10 copies of the business card on a page.
When you go to print, choose to enable crop marks. The crop marks should print on the remaining area of your 8.5" x 11" sheet.
Your instructor should provide details on this. Ask him/her about bleeds and margins.
- - I hope this helps - -
(Complain to someone else if it doesn't)