I need help on total number of units sold. Not sure what I'm doing.

During a year, Mark's monthly sales compensation ranged between $21,500 and $29,300 per month and units sold ranged between 1.300 and 2,100 units for those same months. Required: Use the high-low method to determine Mark's monthly salary and commission rate per unit sold and then calculate the total number of units sold in a year when Mark's total compensation amounted to $291,150. (Round your "Commission rate" to 2 decimal places.) Answer is complete but not entirely correct. $ 8,825 Monthly salary Commission rate Total number of units sold 9.75 per unit 29,862 %