Two pipes A and B can fill a tank in 16 hours and 20 hours respectively. They are opened alternatively for 1 hour each. starting with pipe A first. In how may hours with the empty tank be filled?

A

$$17\frac{3}{4}$$

B

$$17\frac{1}{5}$$

C

$$17\frac{3}{5}$$

D

$$17\frac{1}{14}$$