Question 5738
if the crew can do the job in 60 days, then each day, 1/60th of the job is complete.
each of the 6 men are performing 1/6th of the 1/60th of the work, or 1/360th of the work.
so if the crew is increased by 2 men (1/3 of 6 = 2), they are collectively performing 8/360th of the work.

if we divide 360 by 8, the result is 45 days.  

The original construction was going to take 60 days, now it will take 45 days, so the amount of time saved will be 60-45 or 15 days.