Microft Rentals supplies power tools for special projects. They charge $210 per day for jack hammers, $250 per day for generators, and $400 per day for tractors. The maintenance costs for the jack hammers run $25 per day rented. The generators cost $30 per day and the tractors $32 per day. The company needs to earn at least $25,040 per day on its rentals to stay in business. The company only has 20 tractors that can be rented at one time. It also always has at least twice as many generators rented as jack hammers. Assuming the company is renting enough to stay in business, what combination of rentals would minimize its maintenance costs?