Druid Company makes a single product and uses a standard costing system that applies overhead on the basis of direct labor hours. They recently used 2,000 labor hours to produce 400 units. Their static budget indicated expectations of 500 units, 2,000 DLH and $70,000 in variable overhead. Actual VOH totaled $40,000. What was the variable overhead efficiency variance? Please indicate favorable variances with an "f" and unfavorable variances with a "u" (Round to the nearest dollar at the end of your calculations)