Curt can be paid in one of two ways for the furniture he sells. Plan​ A: Salary of ​650$ per​ month, plus a commission of​ 10% of sales. Plan​ B: Salary of 750​$ per​ month, plus a commission of​ 15% of sales in excess of 5000​$. For what amount of monthly sales is plan B better than plan​ A, assuming​ Curt's sales are always more than 5000​$​?

you want

750 + 0.15(x-5000) > 650 + 0.10x
x > 13000