The students in history class took a final exam and then took equivalent forms of the exam at monthly intervals thereafter. The average score S(t), as percent, after t months was found to be given by the function:

S(t) = 78-15 log(t+1), t0

(a) What was the average score when the sudents initially took the test, t=0?

(b) What was the average score after 4 months?