A takes 4 times as much time as B or 5 times as much time as C to finish a piece of work. Working together, they can finish the work in 4 days. B can do the work alone in:

Answer: Option A

Efficiency of A : B : C = 1 : 4 : 5
Total work = 4(A + B + C) = 4 × 10 = 40
B can do alone work in = $$\frac{40}{4}$$ = 10 days