If 3 men or 4 women can plough a field in 43 days, how long will 7 men and 5 women take to plough it?

Answer: Option D

3 men or 4 women can plough the field in 43 days
3 men = 4 women
1 man = $$\frac{4}{3}$$ women
7 man = $$\frac{28}{3}$$ women
7 men and 5 women = $$5+\frac{28}{3}$$  = $$\frac{43}{3}$$ women
4 women can plough field in 43 days
So,
1 women can plough in = 43 × 4 days
Hence,
$$\frac{43}{3}$$ women can plough = $$\frac{43\times 4\times 3}{43}$$   = 12 days