A and B together can do a piece of work in 12 days, while B alone can finish it in 30 days. A alone can finish the work in :

[A]15 days

[B]18 days

[C]20 days

[D]25 days

**20 days**

A’s 1 day’s work

So, A alone will complete the work in 20 days.

Hence option [C] is correct answer.