Efficiency of a man is 25% more than that of a woman.

Solution

Let the efficiency of a woman be '4e' units/day.
Then, efficiency of a man = (5/4) × 4e = '5e' units/day.

ATQ;

(2n + 4) × 6 × 15 × 5e = (3n - 2) × 5 × 18 × 4e

Or, (2n + 4) × 450e = (3n - 2) × 360e

Or, 900n + 1800 = 1080n - 720

Or, 1800 + 720 = 1080n - 900n

Or, 2520 = 180n

Or, 'n' = 14

Total work = (2n + 4) × 6 × 15 × 5e = (2 × 14 + 4) × 6 × 15 × 5e = 32 × 6 × 15 × 5e = '14400e' units

So, required number of days to complete the work = 14400e ÷ [(10 × 5e + 10 × 4e) × 8] = 14400e ÷ (90e × 8) = 14400e ÷ 720e = 20 days