Cadavieco Detailing's cost formula for its materials and supplies is $1,990 per month plus $8 per vehicle. For the month of November, the company planned for activity of 92 vehicles, but the actual level of activity was 52 vehicles. The actual materials and supplies for the month was $2,440. The activity variance for materials and supplies in November would be closest to: Select one: a. $286 U b. $320 U c. $286 F d. $320 F