30 women are employed to do piece of a work in 20 days. After 5 days, 4 men joined them and finish the work on time. If the efficiency of a man is thrice the efficiency of a women, then find the number of days which will be required to finish the work if extra men didn't join.

Work completed in first 5 days by 30 women = 30 x 5 = 150 woman-days. Remaining work = 600 - 150 = 450 woman-days. After 5 days, 4 men join. Since 1 man = 3 women, 4 men = 12 women. Total workforce for remaining 15 days = 30 + 12 = 42 women-equivalent. Work done in 15 days = 42 x 15 = 630 woman-days. This exceeds the remaining 450, so they finish early. If no men joined, only 30 women would work. After 5 days (150 done), 450 woman-days remain at 30 per day = 15 more days. Total = 5 + 15 = 20 days would be needed. Wait - let me recalculate. They finished ON TIME (day 20) with men helping. So 30 x 5 + 42 x 15 = 150 + 630 = 780 woman-days of capacity was used, but only 600 was needed. The question asks how long without men. Without men: 600 / 30 = 20 days total. But they finished in 20 days WITH men helping. This means the original schedule was already 20 days. If they finished on time with men, that means they were ahead of schedule but used the extra capacity. Without men: they'd need 26 days total. Answer A is correct.