Dubberly Corporation's cost formula for its manufectuing ovethead is $31.400 per month plus $56 per machine-hour. For the month of March, the compary planned for activity of 8,060 machine-hour5, but the actual level of actlvity was 7,960 machine-hours. The actual manufocturing overhead for the month was $506,130. The actlvity variance for manufacturing overivesd in March would be closest to: Multiple Choice $5,600F $23,370U $5,600U $23,370F