K can finish the work in 18 days and L can do the same work in 15 days. L worked for 10 days and left the job. In how many days, K alone can finish the remaining work ?

L's 10 days work =  $\frac{1}{15}\times 10=\frac{2}{3}$

Remaining work =  $1-\frac{2}{3}=\frac{1}{3}$

Now,  work is done by K in one day = 1/18

1/3 work is done by K in   $18\times \frac{1}{3}$ = 6 days