Final answer:
The delivery person can bring up 15 boxes of books at one time in the service elevator.
Step-by-step explanation:
To determine how many boxes of books a delivery person can bring up in a service elevator, we need to consider the maximum capacity of the elevator, the weight of the delivery person, and the weight of each box of books. The maximum capacity of the elevator is 860 pounds and the delivery person weighs 70 pounds. This leaves us with 860 pounds - 70 pounds = 790 pounds of capacity for the boxes of books.
Since each box of books weighs 50 pounds, we'd divide the remaining capacity by the weight of one box to find out how many boxes can be brought up at one time:
790 pounds / 50 pounds per box = 15.8 boxes
Since the delivery person cannot bring a fraction of a box, the maximum number of whole boxes that can be carried up at one time is 15.