2=6
4=8
6=10
8=12
I added +4 for each
Help with what? I am not sure what other question you asked that you need help on. What is the question?
The cotangent function is defined as the ratio between cosine and sine of a given angle, i.e.

Since you can't have zero at the denominator, the cotangent function is not defined when the sine is zero.
Let's look at your option:
, so the cotangent is defined here
, so the cotangent is not defined here
, so the cotangent is defined here
, so the cotangent is defined here