First, add up the 4 sales J. made: 1200+2350+975+375 = 4900 (dollars).
He receives a 4% commission on sales, which here is 0.04($4900) = $196.
His hourly earnings are ($12.75)(x), and x = 6 hours here; thus: $76.50
Add together his earnings ($76.50) and his commission income ($196).
Result: $76.50 + $196 = $272.50 was his income for the day.