YAAS! I literally learned this just a few weeks ago. (I am not actually a high school senior) First, convert 7% to a decimal, which is 0.07. Then multiply 0.07 by 23,000, giving you 1,610. This is your unit rate. I will though, need you to be more specific on "compounding quarterly" because I actually do not know what that means.
The given sequence is
a₁, a₂, ...,

Because the given sequence is an arithmetic progression (AP), the equation satisfied is

where
d = the common difference.
The common difference may be determined as
d = a₂ - a₁
The common difference is the difference between successive terms, therefore
d = a₃ - a₂ = a₄ - a₃, and so on..
The sum of the first n terms is

Example:
For the arithmetic sequence
1,3,5, ...,
the common difference is d= 3 - 1 = 2.
The n-th term is

For example, the 10-term is
a₁₀ = 1 + (10-1)*2 = 19
Th sum of th first 10 terms is
S₁₀ = (10/2)*(1 + 19) = 100
B, 4% .
Find this by using the Interest Formula:
I = P X R X T
I = 7500 X .OO4 X 3
I = 900
The correct answer should be :
Option 3 : 
Hope this helps,
Davinia.