At a shipping warehouse, a manager has purchased two warehouse automation robots, an autonomous mobile robot (AMR) and a preprogrammed aerial drone. The AMR can retrieve 17 packages per hour, and its operating cost is $3.50 per hour. The aerial drone can retrieve 28 packages per hour, and its operating cost is $5.25 per hour. For each hour of operation, the two robots require technicians to perform maintenance and calibration. The technicians usually spend 5 minutes to perform maintenance on the AMR after each hour of operation, while the drone requires 12 minutes of maintenance after each hour. The technicians also work on other warehouse machinery and can only spend 100 minutes per day to maintain the two robots.

a. If the warehouse has at least 250 packages to be retrieved each day, how many hours per day should the manager operate the AMR and drone to minimize the total operating cost? What is the lowest operating cost?

b. If the warehouse manager wants to make sure that each robot is used for at least 4 hours per day, how many hours per day should each robot be used?

c. Based on the answer from part b, identify binding and nonbinding constraints and report the surplus value as applicable.