8. The temperature (in °F) in Boston over a 12-hr period on a certain December day was given by
T = -0.05t3 + 0.4t2 + 3.8t + 5.6 (0 ≤ t ≤ 12)
where $t$ is measured in hours, with t = 0 corresponding to 6 a.m. Determine the average temperature on that day over the 12-hr period from 6 a.m. to 6 p.m. (10 分)
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