Acme Mfg., Inc. produces 3 types of lawn tractor in one of its several plants, Mitymite, All-purpose and Powerhouse. In terms of labor used, Mitymite needs 3 hours for parts acquisition, 2 hours for assembly and 1 hour for packaging and shipping. All-purpose needs four hours for parts acquisition, three hours for assembly and two hours for packaging and shipping. At last, Powerhouse needs four hours for parts acquisition, six hours for assembly and two hours for packaging and shipping. If Acme has available the total of 560 hours of labor for parts acquisition, 520 hours for assembly and 240 hours for packaging and shippping and management wishes all of the hours in each category of labor utilized in that category in production of the very popular tractors, how many Powerhouses must be made so no unused time is left over?