I think it is because they are both different differences
Oh I get this.
So what you have to do is leave the same denominator and just count. Once a fraction has the same numerator and denominator that means it is a whole number.
Given:
Consider the given equation is

To find:
The values of x.
Solution:
We have,

Taking square root on both sides, we get


Adding 18 on both sides, we get


Now,
and 
and 
Therefore, the correct option is A.