A copper extraction company in South Africa extracts copper from two sources: P and N. For optimum capacity utilization, the extraction company’s plant should process at least four tons of copper ore per day. The cost per ton to process the ore from source P is $16, and the cost per ton to process the ore from source N is $8. As the company has only a limited amount of cash available, processing cost cannot exceed $64 per day. In addition, because of governmental regulations, the amount of ore extracted from source N should be less than or equal to twice the amount of ore extracted from source P. If the ore from source P yields 3 ounces of copper per ton, and the ore from source N yields 4 ounces of copper per ton, and the objective is to maximize the amount of copper extracted:

1. Formulate this problem as a linear programming problem.

2. Solve this problem using the graphical method, and provide the optimal solution values of all variables.