I need detailed help with steps on how to solve, please show how each number is calculated. Thanks in advance.

Blake Company produces a single product. Last year, Blake's net operating income under absorption costing was $3,600 lower than under variable costing. The company sold 10,000 units during the year, and its variable costs were $9 per unit which included $1 in variable selling expense. If production cost was $11 per unit under absorption costing, then how many units did company produce during the year ?

A) 8,200 B) 8,800 C) 11,200 D) 11,800 E) None