$1,380 per month and a commission of 7.5% can be translated to
$1,380 + 7.5s, s = sales made within the month
salesperson has a paycheck of $4,132.50
$4,132.50 = $1,380 + 7.5s
4,132.50 - 1380 = 1,380 + 7.5s - 1380 --- Subtract 1380 from both sides
2752.5 = 7.5s --- Simplified
(2752.5)/7.5 = (7.5s)7.5 ---Divide both sides by 7.5
367 = s