#### Explanation:

You can think in term of divisions:
If we call the entire amount $100$, the commission is $2.5$ of it, while for $18 , 500$, corresponds to $x$ and so it must be:
$\frac{100}{2.5} = \frac{18 , 500}{x}$
Rearranging:
x=(18,500×2.5)/100=\$462.5

Hope it helps!