Cost of public colleges. the average cost, in dollars, for tuition and fees for in-state students at four- year public colleges over the period 2000-2014 can be modeled by the equation y = 4.065x2 + 370.1x + 3450 where x = 0 corresponds to 2000, x = 1 corresponds to 2001, and so on. based on this model, for what year after 2000 was the average cost $8605? (source: the college board, annual survey of colleges.)