Verified answer

Let's do this in two steps.

150 workers can build 12 miles of highway in 14 weeks.

125 workers can therefore build 12 miles of highway in 150/125 * 14 weeks = 16.8 weeks.

Note that it takes longer for fewer people to do the same amount of work.

125 workers can build 15 miles of highway in 15/12 * 16.8 = 21 weeks.

You have the equation t = k L/w where k is a constant with units of weeks(workers)/miles.

14 wk = k 12/150 so k = 14(150)/12 = 175

You want 175(15) / 125 weeks

Workers....Miles...Weeks

150.........12........14

125........15.......?

150/125 X 15/12 X14 =

1.2 X 1.25 X 14 = 21 weeks ANSWER