Answer:
Hello,
I am not sure if you are still having an issue with this problem but for future reference for you or anyone else the answer is
d. Each vertical line drawn through the graph will intersect a function in only one location.
I thought of it this way:
"Each vertical line" which tells me only one line per "one location" now I could be completely off but this was just my logic and it helped me personally.
Answer:

0.16
Step-by-step explanation:
According to the question the mathematical model should be

Differentiating with respect to time we get

So, the rate of change of brightness after t days is 
After 1 day means 

The rate of increase after one day is 0.16.
Answer:
When we have a function y = f(x)
The set of the possible values of x is called the domain, and the set of the possible values of y is called the range.
In this case, we have:
x = age, and y = price.
x y
< 5 $0
5 - 17 $25
18 - 64 $40
≥ 65 $35
Then the range is the possible age of the customer, and it goes for all the possible ages (as whole numbers)
So the domain will be the set of all the positive integers:
D = {1, 2, 3, 4, 5, ...}
(of course, we can not have an age equal to 1300 or infinity, but we really can not cap the domain)
The range is the possible values of y, in this case is discrete, because we have only 4 possible prices, so the range is:
R = {$0, $25, $40, $35}