$A$ can do a piece of work in $14$ days which $B$ can do in $21$ days. They begin together but $3$ days before the completion of the work, $A$ leaves off. The total number of days to complete the work is :

- $\frac{33}{5}$
- $8\frac{1}{2}$
- $\frac{51}{5}$
- $13\frac{1}{2}$