Explanation

First, let's find the work rate of 10 men:

10 men construct 75 km in 5 days, so:

Work rate = 75 km / 5 days = 15 km/day for 10 men

Now, let's find the work rate for 15 men:

Work rate for 15 men = (15/10) × 15 km/day = 22.5 km/day

Now, let's find the time needed for 15 men to construct 45 km:

Time = Distance / Work rate

= 45 km / 22.5 km/day

= 2 days