Corrington Manufacturing Company prepared a fixed budget of 80,000 direct labor hours, with estimated overhead costs of $400,000 for variable overhead and $120,000 for fixed o verhead. Corrington then prepared a flexible budget at 78,000 labor hours. How much is total overhead costs at this level of activity? a. $440,000 b. $400,000 c. $510,000 d. $520,000