8 men and 8 boys can finish a piece of work in 10 days. 9 women and 7 boys can finish the same work in 10 days. Also 7 men and 6 women can finish the same work in 10 days. In how many days 1man, woman and one boy can finish the work, at their double efficiency? a) 25 days b) 20 days c) 15 days d) 10 days