Word problem on combined variation

Question

Suppose that the number of cars manufactured at an automobile plant varies jointly as the number of workers and the time they work. If 85 workers can produce 136 cars in 8 hours, find the number of workers that can produce 175 cars in 7 hours.

Answer 1

85 produce 136 cars in 8 hours

125 workers produce 175 cars in 7 hours

workers are directly related to the number of cars, and inversely related to the number of hours

W = kC/H

85 = k(136)/8= 17k

k = 85/17

W = (85/17)C/H

W = (85/17)175/7 = 125