When i didn't like fractions why is the numerator the only part of the faction that changes

To understand fractions you have to understand that any part of it can change.

1/2 = 2/4 = 4/8 = 8/16 = infinity same fractions
^ the reason these are all equal is because BOTH the numerator and denominator changes.

The only time the denominator doesn't change, and numerator does is when you add:

For example, 5/8 + 2/8 = 7/8 , you only add the numerators
For a fraction to be able to add to another fraction the denominator has to stay the same

A WRONG ANSWER would be to add BOTH , 5/8 + 2/8 = 7/16 <- This is wrong

It’s going to be d. 4x^2-4x-19’