Three machines fill 40 boxes in an hour. One machine can fill 40/3 boxes in an hour. Following the second part of the problem, one machine would take 150/40/3 = 11.25 hours to fill 150 boxes. Machines and time are inversely proportional. Then, it would take 11.25 * 1/5=2.25 hours for 5 machines to fill 150 boxes.
