Assume that a company's planned level of acthity was 3,500 units and its actual level of activity was 3,000 units. The variable portion of one of the company's mixed costs included in its flexble budget was $2,100. The cost formuto for the variabte portion of the mixed cort that ine company uses for budgeting putposes is: Mulvole choice $070 per unit $0.60 per unit $1.67 perunit. 51.43 per unit