Students in an English class took a final exam. They took equivalent forms of the exam at monthly intervals thereafter. The average score S(t), in percent, aftert months was found to be given by
S(t) = 68 - 20 log (t + 1), t ≥ 0.
a) What was the average score when they initially took the test, t = 0?
b) What was the average score after 14 months?
c) After what time t was the average score 40%?