Answer:
a. 
b. 
Step-by-step explanation:
First, we need tot find a general expression for the amount of caffeine remaining in the body after certain time. As the problem states that every hour x percent of caffeine leaves the body, we must substract that percentage from the initial quantity of caffeine, by each hour passing. That expression would be:

Then, to find the amount of caffeine metabolized per hour, we need to differentiate the previous equation. Following the differentiation rules we get:

The rate is negative as it represents the amount of caffeine leaving the body at certain time.
Answer:
y = 6
Step-by-step explanation:
Its going by 6's
To solve, simply do this:

Then you'll get the answer, -7/16
Pi r2
17 divide 2=8.5
Then
8.5•8.5=72.25
Then
3.14•72.25=226.865
Then
226.865 divide by 2 =113.4325m2