Consider a process consisting of three resources. Assume there exists unlimited demand for the product, and that all activities are always performed in the following sequence. Resource 1 has a processing time of 7 minutes per unit. Resource 2 has a processing time of 4 minutes per unit. Resource 3 has a processing time of 6 minutes per unit. All three resources are staffed by one worker and each worker gets paid $13 per hour. What is the cost of direct labor?

A. $13.00 per unit

B. $4.55 per unit

C. $52 per unit

D. $91 per unit