He can carry around 6 boxes. How? So add one box of books and himself. You should get 210 lb. Afterwards, do 1,400 lb / 210 lb, since the max capacity of the elevator is 1,400 lb. You will get 6.666 and repeating. It will only be 6 boxes at one time. Do NOT round the decimal. The elevator will not be able to take 7 boxes PLUS himself. Otherwise the elevator will crash and fall. Hope this helped!