Without any calculations it's evident it can't be neither B (both numbers are even, so they're divisible by 2) nor C (the numbers end in 0 and 5, so they're divisible by 5).
A.

Both numbers have a factor of 3, so they're not relatively prime.
That means it must be D. But, let's check it.

Indeed, those two numbers are relatively prime.
Given the function:

Let's find the amplitude and period of the function.
Apply the general cosine function:

Where A is the amplitude.
Comparing both functions, we have:
A = 1
b = 4
Hence, we have:
Amplitude, A = 1
To find the period, we have:

Therefore, the period is = π/2
The graph of the function is shown below:
The parent function of the given function is:

Let's describe the transformation..
Apply the transformation rules for function.
We have:
The transformation that occured from f(x) = cosx to g(x) = cos4x using the rules of transformation can be said to be a horizontal compression.
ANSWER:
Amplitude = 1
Period = π/2
Transformation = horizontal compression.
She can buy a maximum of 12 books for her music class
Answer:
I have attached the work to your problem.
Please see the attachment below.
I hope this helps.
Vertex is (4,-3) and the axis of symmetry is X=4