I need detailed help with steps to find solution and why answer which was C) is what it is :

Gladstone Footwear Corporation flexible budget cost formula for supplies, a variable cost, is $2.83 per unit of output. The company's flexible budget performance report for last month showed a $9,555 unfavorable spending variance for supplies. During that month, 19,500 units were produced. Budgeted activity for the month had been 19,300 units.

Question : The actual cost per unit of indirect materials must have been closest to :

A) $2.83 B) $3.85 C) $3.82 D) $3.81