Chapter 9, Problem 30E

I need help solving this general accounting question with the proper methodology.

Gabbana Manufacturing estimated that machine hours for the year would be 30,000 hours and overhead (all fixed) would be $150,000. Gabbana applies its overhead on the basis of machine hours. During the year, all overhead costs were exactly as planned ($150,000). There was $12,000 in over-applied overhead. How many machine-hours were worked during the period? Help

Accurate answer