A metal-working shop has access to two types of metal-working equipment, a chop saw and a steel cutter. A chop saw can work 25 pounds of steel and generates 25 units of waste every day. A steel cutter can only cut 5 pounds of steel and generates 3 units of waste every day.  The metal-working shop is expecting an increase in demand and must cut 520 pounds of metal every day. However, there is a waste limitation due to the fines that may be in place if too much heavy metal is discarded and they may at most produce 400 units of waste every day. How should the metal-working shop purchase their metal-working equipment to decrease the total number of metal-working equipment needed?