Frogue Corporation uses a standard cost system. The following information was provided for the period that just ended: Actual price per kilogram $3.00 Actual kilograms of material used 31,000 Actual hourly labor rate $18.10 Actual hours of production 4,900 labor hours Standard price per kilogram $2.80 Standard kilograms per completed unit 6 kilograms Standard hourly labor rate $18.00 Standard time per completed unit 1 hr. Actual total factory overhead $34,900 Fixed factory overhead $18,000 Standard fixed factory overhead rate $1.20 per labor hour Standard variable factory overhead rate $3.80 per labor hour 100% of normal capacity 15,000 hours Plant operated during the period 10,000 hours Units completed during the period 5,000 The total factory overhead cost variance is: a. $3,900 favorable b. $8,100 favorable c. $9,900 unfavorable d. $8,100 unfavorable