Students in a fifth-grade class were given an exam. During the next 2 years, the same students were retested several times. The average score was given by the model
f(t)=81-12log(t+1),0<t<24
where tis the time in months round answer to 1 decimal point.
(a) What is the average score on the original exam? _____________
(b) What was the average score after 6 months?______________
(c) What was the average score after 18 months?_______________