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.
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Solution:
1) Distribute
12a+12b
Done!
Answer:
Associative
Step-by-step explanation:
The associative property of addition states that you can add numbers however they are grouped inside parentheses.
It doesn't matter where you put the parentheses. You will always get the same answer.
For example,
