a utilities company sells electrical wiring at $7 per 15 meters, which costs them $3 per 15 meters. if a customer purchases at least 300 meters, the company offers a 10% discount with an additional 5% discount for every 300 additional meters, such that 650 meters would receive a discount of a 15%. They must sell less than what length of wire if they wish to have at least a 40% profit margin?