Suppose that the amount of time it takes to build a highway varies directly with the length of the highway and inversely with the number of workers. Suppose also that it takes 150 workers 14 weeks to build 12 miles of highway. How long will it take 125 workers to build 15 miles of highway?
T = kL/w^2
so, Tw^2/L is constant
You want T such that
125^2 * T /15 = 150^2 * 14 / 12