Here are the formulas for the Peapod shopping assignment:
Cell  | Formula  | 
Total Price  | =Price x Quantity  | 
Unit Price  | =Price/Amount  | 
Amount Needed  | =# of students in class x amount on shopping list  | 
Amount Purchased  | =Quantity x Amount  | 
A13  | =D10/B13  | 
A16  | =B13*5  | 
B16  | =A16-D10  | 
C16  | =B16/B13  |