An amazon warehouse has three different drones to deliver products to its customers. The drone A can deliver 10 products per hour, at operating cost of 2$ per hour. The drone B can deliver 18 products per hour, at operating cost of 5$ per hour. The drone C can deliver 15 products per hour, at operating cost of 3$ per hour. The maintenance times per hour of operation are 10 minutes, 15 minutes, and 12 minutes respectively for drones A, B and C. The technicians can only spend 500 minutes per day to maintain these drones. Each drone can be operated for a maximum of 15 hours per day. If the warehouse must deliver at least 500 products per day, how many hours should the manager operate these drones to minimize operating costs?

I'm struggling with getting this problem into an equation(s) I can solve.