A paper mill prouduces two grads of paper viz., X and Y. Becouse of raw material restriction, it cannot product more then 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 200 and 500 per ton of grade Xand Y paper respectively. Formulate this as a Linear programming problem