A paper mill produces two grades of paper viz, x and y. Because of raw material restrictions, it cannot produce more than 400 tons of grade X paper and 300 tons of grade Y paper in a week. There are 160 production hours in a week. It requires 0.20 and 0.40 hours to produce a ton of grade X and Y papers.The mill earns a profit of rs.200 and rs.500 per ton of grade X and Y paper respectively. Formulate this is a linear programming problem.