Without doing any math, you can intuitively rationalize the answer. Since two men and 4 women take the same amount of time for the same work, this means that the 2 men are equivalent to the 4 women when it comes to this particular work. This means that each man is equivalent to 2 women. For the 2 men, replacing 1 man with 2 women gives you a total of 1 man and 2 women doing the same work in 2 hrs. I hope this helps.