A alone can finish a work in 15 days. A works only for the first two days and last two days. The rest work is done by B and the work is completed in 20 days. In how many days A and B together can finish the work?

A

$$\frac{90}{8}$$

B

$$\frac{80}{7}$$

C

$$\frac{80}{9}$$

D

$$\frac{70}{8}$$