Quack Co. was analyzing variances for one of its operations. The initial budget forecast production of 20,000 units during the year with a variable manufacturing overhead rate of $10 per unit. Quack produced 19,000 units during the year. Actual variable manufacturing costs were $210,000. What amount would be Quack's flexible budget variance for the year?
a. $10,000 favorable
b. $20,000 favorable
c. $10,000 unfavorable
d. $20,000 unfavorable