x does $$\frac{1}{4}$$ of a job in 6 days. y completes rest of the job in 12 days. Then x and y could complete the job together in = ?

x does $$\frac{1}{4}$$ work in 6 days.
∴ x does complete work in 6 × 4 = 24 days
y does complete the $$\frac{3}{4}$$ work in 12 days.
∴ y does complete work in 12 × $$\frac{4}{3}$$ = 16 days
x and y together can complete a work in
$$\eqalign{ & = \frac{{16 \times 24}}{{16 + 24}} \cr & = \frac{{48}}{5} \cr & = 9\frac{3}{5}\,{\text{days}} \cr} $$