The Standard & Poor's (S&P) 500 index during the period 2008-2018 is given by

I(t)= 3 t² - 71 t + 1922 (8 t 18)

(t= 8 represent 2008)

What was the average rate of change of the S&P index during the period from 2008 to 2010? Result (points per year):______________

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