According to the formula, if pipe A can comletely fils a tank in x hours and pipe B can comletely empty the tank in y hours, then the time taken by both pipes together to fill the tank is $\frac{\mathrm{xy}}{\mathrm{x}-\mathrm{y}}$ hours.

So, $\frac{14\times 18}{18-14}=\frac{252}{4}=63 \mathrm{hours}$

The tank will be filled by both the pipe opened simultaneously in 63 hours

Hence option B is correct