Students in a mathematics class took an exam and then took a retest monthly with an equivalent exam. The average scores for the class are given by the human memory model
f (t) = 80 ˆ’ 17 log(t + 1), 0 ‰¤ t ‰¤ 12 where t is the time in months.

(a) Use a graphing utility to graph the model over the specified domain.
(b) What was the average score on the original exam (t = 0)?
(c) What was the average score after 4 month?
(d) What was the average score after 10 month?