A can do a certain work in 18 days and B can do it in 30 days. They work together for 6 days. The remaining work is completed by C alone in 7 days. In how many days will A, B and C together complete the same work?

A

$$9\frac{3}{7}$$

B

$$11\frac{3}{7}$$

C

$$6\frac{3}{7}$$

D

$$7\frac{3}{7}$$