Petrus Framing's cost formula for its supplies cost is $1,830 per month plus $10 per frame. For the month of March, the company planned for activity of 623 frames, but the actual level of activity was 629 frames. The actual supplies cost for the month was $8,540. The activity variance for supplies cost in March would be closest to: Multiple Choice $480 F $480 U $60 U $60 F