Minhaz and Alam can complete a work in 18 days . After working together for 12 days Minhaz stops and Alam competes the remaining work in 8 days. In how many days can Minhaz complete the work if he works alone?

In 18 days, they can complete = 1 parts of work 

In 1 days, they can complete= $\frac{1}{18}$ parts of work

In 12 days, they can complete = $\frac{12}{18}=\frac{2}{3}$ parts of work 

Remaining work  $=\left(1-\frac{2}{3}\right)=\left(\frac{3-2}{3}\right)=\frac{1}{3}$

Now,$\frac{1}{3}$ parts of work is done by Alam in = 8 days 

1 or complete parts of work is done by Alam in= $8 \times 3 = 24 days$

Alam can do $\frac{1}{24}$ parts of work in 1 day.

Minhaz can do in 1 day =$\left(\frac{1}{18}-\frac{1}{24}\right)=\left(\frac{4-3}{72}\right)=\frac{1}{72}$ parts

That means $\frac{1}{72}$ parts of work is done by Minhaz in 1 day

1 or complete parts of work is done by Minhaz in $\frac{72\times 1}{1}=72 day$

He can do the whole work alone in 72 days. ans.