According to the formula, If pipe A  and B fills a tank in x and y hours respectively, but a third pipe C empties the full tank in z hours then the net portion filled in 1 hour when all of them are opened together is $\frac{\mathrm{xyz}}{\mathrm{yz}+\mathrm{xz}-\mathrm{xy}}$ hours.

So,

 $$\begin{gathered} \frac{10\times 16\times 32}{(10\times 32)+(16\times 32)-(10\times 16)} \\ =\frac{5120}{672}=\frac{160}{21} \mathrm{or} 7\frac{13}{21}\mathrm{hours} \end{gathered}$$

The tank will be filled in $7\frac{13}{21}$ hours when all the pipes are opened simultaneously.

Hence option B is correct