The average cost of tuition and fees at public four year colleges in the United States can be modeled by the formula
where T represents the average cost of tuition and fees for the school year ending x years after 1996. Use the formula to determine the year when tuition and fees at public U.S. colleges average $4421.
(Note: Give the year. For example, if you calculate that the answer is 9 years after 1996, then enter 2005 .)