A can do a piece of work in 18 days. He worked at it for 12 days and B finished the remaining work in 8 days. B alone can do the whole work in ?

$$\eqalign{ & {\text{18A}} = {\text{12A}} + {\text{8B}} \cr & {\text{6A}} = {\text{8B}} \cr & \frac{{\text{A}}}{{\text{B}}} = \frac{4}{3} \cr & {\text{So, }} \cr & {\text{Efficiency of A and B are }}4,3. \cr & {\text{Total work}} \cr & = 18 \times 4 \cr & = 72{\text{ units}} \cr & {\text{So, B will do}} \cr & = \frac{{72}}{3} \cr & = 24{\text{ days}} \cr} $$