algebra
posted by selina on .
students in a biology class just took a final exam. a formula for predicting the average exam grade on a similar test t months later is.
s(t)=7815log(t+1)
(a)find the students average score when they first took the final exam.
(b)what would be the expected average score be on a retest after 4 months.

I know the answers I just am not sure how to work the problem to get them.
(a)78
(b)67.5
Please help me with the working of these problems.
Thank you