Math

The idea is just try to make  a square number inside the sqrt.

 

49 no good cuz 63-49 not divisible by 3, and the way to check for the rest that doesn't work or works is to see whether it's divisible by 3 or not.

36 works for x = 81

25 no good

16 no good

9 works for x = 324

4 no good

1 no good.

 

Real Values can only be x = 81 or x = 324, so answer is 2.