Raju, Shobh and Mohan can do a work in 15 days, 20 days and 25 days respectively. In how many days,will the work be finished, if they do it on alternate days?

A

$$15\frac{9}{10}$$ days

B

$$18\frac{7}{10}$$ days

C

$$21\frac{7}{10}$$ days

D

$$18\frac{9}{10}$$ days