Assume that the cost formula for one of a companys mixed expenses is $10,000 + $3.90 per unit. The companys planned level of activity was 2,000 units and its actual level of activity was 2,170 units. The actual amount of this expense was $18,200. The activity variance for this expense is: Multiple Choice $1,663 U. $663 U. $63 U. $600 F.