Curt can be paid in one of two ways for the furniture he sells. Plan A: Salary of $800 per month, plus a commission of 10% of sales. Plan B: Salary of $900 per month, plus a commission of 15% of sales in excess of $6000. For what amount of monthly sales is plan B better than plan A, assuming Curt's sales are always more than $6000? Plan B is better than Plan A when Curt's sales are more than $