A delivery person uses a service elevator to bring boxes of books up to an office. The delivery person weighs 170 lb and each box of books weighs 40 lb. The maximum capacity of the elevator is 920 lb. How many boxes of books can the delivery person bring up at one time?
If you subract the persons weight by the maximum capacity of the elevator you have the total weight which can be "filled" by books. If you then divide this number by the weight of a box of books you'll have the number of boxes of books he could bring.
let x be number of books.
x= 18.75 boxes.
Techincally that means he'll probably only bring 18 boxes or 18 boxes and one which is 3/4 filled with books.