Pipe A can fill a tank completely in 5 hours. However, on account of a leak at the tank, it takes 3 more hours to fill the tank. How long will the leak take to empty the full tank when pipe A is closed/shut ?

Pipe A takes 5 hours to fill the tank. Therefore, it fills one-fifth the tank in an hour or 20% of the tank in an hour.
When there is a leak it takes 8 hours more for the tank to fill i.e. one-eighth or 12.5% of tank is filled in 1 hour.
On account of the leak , 20% - 12.5% = 7.5% water gets wasted every hour.
$$\frac{1}{x}$$ = $$\frac{1}{5}$$ - $$\frac{1}{8}$$
x= $$\frac{40}{3}$$ hours.
Hence , it takes 13 hours 20miutes to empty the tank.