A merchant plans to sell two types of personal computer - a desk top model and a portable model that will cost Rs. 25,000 and Rs. 40,000 respectively. He estimates that the total monthly demand of computers will not exceed 250 units. Determine the number of units of each type of computers which the merchant should stock to get a maximum profit if he does not want to invest more than 70 lakh and if his profit on the desktop model is Rs. 4,500 and the portable is Rs. 5,000.