A and B together can do a piece of work in 9 days, while B and C together can do it in 15 days. All three working together can complete the work in 6 days. In how many days will A and C together complete the work ?
1
\(6 \dfrac{1}{7}\)
2
6
3
\(6 \dfrac{4}{7}\)
4
\(6 \dfrac{3}{7}\)