Im having a little trouble coming up with an equation to find maximum gross income.

A television company agrees to establish a community antenna in a new suburb at a charge of $25 each for 1000 subscribers or less. To encourage more subscribers, it is agreed to give a discount of 10 cents to each subscriber for every additional 10 subscribers in excess of 1000. For the company to make the most income what number of subscribers should it have?

Any help would be greatly appreciated!