Dermody Snow Removal's cost formula for its vehicle operating cost is $2,900 per month plus $320 per snow-day. For the month of December, the company planned for activity of 15 snow-days, but the actual level of activity was 13 snow-days. The actual vehicle operating cost for the month was $7,980. The spending variance for vehicle operating cost in December would be closest to:
a. $280 U
b. $280 F
c. $920 U
d. $920 F