Solve it by Linear Programming

A fertilizer manufacturer has just received a contract to supply 10,000 tons of 31212 fertilizer. The guaranteed composition of this fertilizer is (by weight) at least 3% nitrogen, 12% phosphorus and 15% potash. The fertilizer can be mixed from any combination of the raw materials described in the table below. The raw materials are purchased per ton. The fertilizer company also has an option to purchase 3-12-12 fertilizer from another company at $19.50/ ton. Assuming the cost of mixing and transportation is zero, should the company buy fertilizer from the second company or mix their own? If the company should mix their own fertilizer, what is the proportion of each ingredient