need help with this. thank you

10. A typical cup of coffee contains 100 mg of caffeine. Every hour approximately 16% of the amount of caffeine is metabolized in the body and eliminated (a) (4 points) Write a function equation M(t) = a(b)* that will represent the amount of caffeine in the body after t hours. (b) (4 points) Determine the amount of caffeine that is in the body after 4 hours as- suming the person had one cup of coffee