Ehh, now it's letting me answer.
So the associative property is basically as long as it's addition or multiplication, you can move around the groupings and it will still be the same.
For example, you can say:(21 * 7) (3x) instead of (21)(7)(3x)
And it would be equal to the old version.
(To answer your other question, the commutative property is you can move around all the parts of the equation as long as it's addition or multiplication.)
So basically, it would be the first one you sent me.
Answer:

Step-by-step explanation:

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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.