Explanation:

Total work = number of (man\woman)×time
Four men and 6 women can complete a certain piece of work in 5 days whereas three men and 4 women can complete it in 7 days so,
(4m + 6w)×5 = (3m + 4w) × 7
20m + 30w = 21m + 28w
m = 2w
Now,