A local business plans on advertising their new product by purchasing advertisements on the radio and on TV. The business plans to purchase at least 60 total ads and they want to have at least three times as many TV ads as radio ads. Radio ads cost $20 each and TV ads cost $120 each. The advertising budget is $6460. It is estimated that each radio ad will be heard by 900 listeners and each TV ad will be seen by 4500 people. How many of each type of ad should be purchased to maximize the number of people who will be reached by the advertisements?