Assistant with chain rule

8. COST OF WIRELESS PHONE CALLS As cellular phone usage continues to soar, the airtime costs have dropped. The average price per minute of use (in cents) is projected to be f (t) = 31.88(1 + t )-0.45 where t is measured in years and t = 0 corresponds to the beginning of 1998. Compute f (t). How fast was the average price/minute of use changing at the beginning of 2000? What was the average price/minute of use at the beginning of 2000? 9. MALE LIFE EXPECTANCY Suppose the life expectancy of a male at birth in a certain country is described by the function f (t) = 46.9(1 +1.09t)0.1 where t is measured in years, with t =0 corresponding to the beginning of 1900. How long can a male born at the beginning of 2000 in that country expect to live? What is the rate of change of the life expectancy of a male born in that country at the beginning of 2000