My son gave his dad money to buy a piece of heavy equipment for his business.His dad promised a percentage of the profits made using this piece of machinery. His Dad gave him 15,000.00 for his profit and some money back on the equipment as he is paying him back so much a year on it and then the profit he makes will end when dad has paid him back. How does he file this money on his taxes as he has no paperwork other then receipts for it. Thanks