Question

A delivery person uses a service elevator to bring boxes of books up to an office. The delivery person weighs 190 lb and each box of books weighs 40 lb. The maximum capacity of the elevator is 900 lb. How many boxes of books can the delivery person bring up at one​ time?

Answer 1

900-190= 710

710/40= 17.75

17 (or 18, but I would choose 17 if I were you) 

Answer 2

190+40x=900
40x=710
x=17.75
They can only bring up 17 boxes at a time because even though the elevator can handle another 30 pounds that is not the weight of another full box.