4. A refinery manufactures two grades of jet fuel, f1 and Fl, by blending four types of gasoline, A, B, C, and D. Fuel F1 uses gasolines A, B, C, and D in the ratio 1:1:2:4, and fuel Fl uses the ratio 2:2:1:3. The supply limits for A, B, C, and Dare 1000, 1200,900, and 1500 bbllday, respectively.The costs per bbl for gasolines A, B, C, and Dare $120, $90, $100, and

$150, respectively. Fuels F1 and Fl sell for $200 and $250 per bbi.The minimum demand for F1 and Fl is 200 and 400 bbUday. Determine the optimal production mix for F1 and n.