Wall Corporation uses a job costing system. Wall Corporation's selected cost data for July is shown below: Cost of goods manufactured $420,000 Work in process inventory, July 1 $100,000 Work in process inventory, July 31 $120,000 Cost of direct materials used $50,000 Manufacturing overhead cost is allocated at 70% of direct labor cost. What are the total manufacturing costs incurred during July? a. $550,000 b. $520,000 c. $440,000 (1. $400,000