His basic salary is $ 2,500, his commission on sales is 3% (on sales only)
At the end of te month he got $3,040
Let x be the TOTAL sales performed during this month, so the money generated from sales (only) is (x).(3%), Hence the equation:
2500 + (x).(3%) = 3040
2500 + x(0.03) = 3040
x(0.03) = 3040-2500
x(0.03) = 540
and x = 540/0.03
x = $18,000
