If you would like to know the amount of sales that Marcus will be able to pay his bills, you can calculate this using the following steps:
s ... amount of sales
$1500 + 15% of s >= $2430
1500 + 15% * s >= 2430
15/100 * s >= 2430 - 1500
15/100 * s >= 930
s >= 930 * 100/15
s >= $6200
The correct result would be $6200.