Response to the following problem:
Auto Brakes Inc. manufactures brake rotors and has always applied overhead to production using direct labor hours. Recently, company facilities were automated, and the accounting system was revised to show only two cost categories: direct material and conversion. Estimated variable and fixed conversion costs for the current month were $170,000 and $76,000, respectively. Expected output for the current month was 5,000 rotors and the estimated number of machine hours was 10,000. During July 2010, the firm actually used 9,000 machine hours to make 4,800 rotors while incurring $228,000 of conversion costs. Of this amount, $150,000 was variable cost.
a. Using the four-variance approach, compute the variances for conversion costs.
b. Evaluate the effectiveness of the firm in controlling the current month's costs.