Tick (✓) the correct answer:

(a) x

Let the required number be $z$. Then, we have:

$x \%$ of $y=y \%$ of $z$

$\Rightarrow\left(y \times \frac{x}{100}\right)=\left(z \times \frac{y}{100}\right)$

$\Rightarrow \frac{y x}{100}=\frac{z y}{100}$

$\Rightarrow z=\left(\frac{y x}{100} \times \frac{100}{y}\right)$

$\Rightarrow z=x$