P, Q and R can do a work in 10, 15 and 30 days respectively. P works daily. Q and R together join P on alternate days starting the first day. In how many days will the work be done?

A

$$6\frac{1}{3}$$

B

$$6\frac{3}{4}$$

C

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

D

$$6$$