blacktop refining extracts minerals from ore mined at two different sites in montana. each ton of ore type 1 contains 20% copper, 20% zinc and 15% magnesium. each ton of ore type 2 contains 30% copper, 25% zinc and 10% magnesium. ore type 1 costs $90 per ton while ore type 2 costs $120 per ton. blacktop would like to buy enough ore to extract at least 9 tons of copper, 7 tons of zinc, and 6 tons of magnesium in the least costly manner. (let x1