A paper mill produces two grades of paper viz.,x and y. Bacause of raw material restrictions, it cannot produce more than 400 tones of grade x paper and 300 tons of grade y paper in a week. there are 160 production hours in a week. it requires 0.25and 0.40 hours to produce a ton of grade z snf y psprtd. the mill earns a profit of rs.200 and rs.500 per ton of grade x and y paper respectively. formulate this as a linear programming problem.