In the year 2005, the average cost of a car could be modeled by the equation C= -15x^2 + 20x - 3 where x is the number of years since 2005. By the year 2010 the average cost had changed, and the equation could be modeled by C= -10x^2 + 30x - 2. Find the difference in average cost equation for cars between 2005 and 2010.