The Collins Co. uses a predetermined overhead rate based on direct labor cost to apply manufacturing overhead to jobs. For the year ended December 31, Nil's estimated manufacturing overhead was $600,000, based on an estimated volume of 50,000 direct labor hours, at a direct labor rate of $6.00 per hour. Actual manufacturing overhead amounted to $620,000, with actual direct labor cost of $325,000. For the year, manufacturing overhead was: a. overapplied by $20,000. b. underapplied by $22,000 c. overapplied by $30,000 d. underapplied by $30,000