Three persons A, B and C working alone, can complete a piece of work in 10, 15, and 40 days respectively. A and C started  working together, after 5 days, C quits and is replaced by B, The number of days required to complete the work is

A

$$6\frac{1}{2}$$

B

$$8\frac{2}{3}$$

C

10

D

$$7\frac{1}{4}$$