A company's flexible budget for 48,000 units of production showed variable overhead costs of $72,000 and fixed overhead costs of $64,000. The company incurred overhead costs of $122,800 while operating at a volume of 40,000 units. The total controllable cost variance is:
a. 1,200 favorable
b. 1,200 unfavorable
c. 13,200 favorable
d. 13,200 unfavorable
e. 15,200 favorable