The maximum weight the elevation can carry is
Each box weighs
As in the sign is stated that the maximum weight that the elevator can carry is 1000 pounds and each of the boxes of books weighs 60 pounds,you should divide the maximum weight the elevator can carry by the weight of each box of books then you have
He can maximum ride 16.7boxes, but if the boxes can't be divided he can just carry 16 boxes, because if he carries 17 boxes the weight in the elevator will be 1020, which beats the maximum capacity of the elevator.
Hence,
Then he can place a maximum of 16 boxes in the elevator