Let the leak take x hours to empty the tank.

Now part of the tank filled by the inlet in 1 hour is $\frac{1}{8}$

Part filled by (inlet and leak) in 1 hour= $\frac{1}{8+2}=\frac{1}{10}$

As per the question,

$\frac{1}{\mathrm{x}}=\frac{1}{8}-\frac{1}{10}=\frac{5-4}{40}=\frac{1}{40}$

x=40 hours

Hence option D is correct