$220 is a flat amount of his pay, so
$448.50 - $220 = $228.50 represents the amount earned by commission.
So $228.50 is 7.5% of total sales.
Mathematically, this can be expressed
228.50 = 7.5 / 100 x X, where X is the total sales.
Solve for X by multiplying both sides by the inverse fraction 100/7.5:
X = 228.50 x 100 / 7.5
You'll find this matches one of the options!