A telephone company in a town has 500 subscribers on its list and collects fixed charges of Rs. 300 per subscriber. The company proposes to increase the annual subscription and it is believed that every increase of Rs. 1 one subscriber will discontinue the services. Find what increase will bring maximum revenue?

A private telephone company serving a small community makes a profit of Rs. 12.00 per subscriber, if it has 725 subscribers. It decides to reduce the rate by a fixed sum for each subscriber over 725, thereby reducing the profit by 1 paise per subscriber. Thus, there will be profit of Rs. 11.99 on each of the 726 subscribers, Rs. 11.98 on each of the 727 subscribers, etc. What is the number of subscribers which will give the company the maximum profit?