A model for the food-price index (the price of a representative "basket" of foods) between 1984 and 1994 is given by the function

$I(t) = 0.00009045 t^5 + 0.001438 t^4 - 0.06561 t^3 + 0.4598 t^2 - .6270 t + 99.33$

Where t is measured in years since midyear 1984, so $0 \leq t \leq 10$, and I(t) is measured in 1987 dollars and scaled such that I(3)=100. Estimate to two decimal places the times when food was cheapest and most expensive during the 1984-1994 period.

cheapest at t =

most expensive at t =

You can earn partial credit on this problem.