Achal can be paid in one of two ways for the furniture he sells: Plan A: A

Question:

Achal can be paid in one of two ways for the furniture he sells: Plan A: A salary of $900 per month, plus a commission of 10% of sales;
Plan B: A salary of $1200 per month, plus a commission of 15% of sales in excess of $8000.
For what amount of monthly sales is plan B better than plan A if we can assume that Achal's sales are always more than $8000?