Answer: the number of additional boxes that can be lifted in the same load is 20
Step-by-step explanation:
Let x represent the number of additional boxes that can be lifted in the same load.
John has 10 boxes that weigh 13.75 kilograms each, and a number of additional boxes that weigh 15.5 kilograms each. If he puts the 10 boxes on the elevator, it means that the total weight if he adds x additional boxes would be
13.75 × 10 + 15.5x
= 137.5 + 15.5x
Since the sign in the elevator says the elevator can lift up to 450 kilograms, it means that
137.5 + 15.5x = 450
15.5x = 450 - 137.5
15.5x = 312.5
x = 312.5/15.5
x = 20.16