x^2 - 12x + 36 is a perfect square trinomial and can be written as (x-6)(x-6).
(x - 6)^2 = 44.
Take the square root of both sides to get...
x - 6 = ±√44 (Always make the square root + or - when you square root)
Add 6 to both sides...
x = √44 + 6
x = -√44 + 6
These are the 2 values of x.
You can also write it to be -0.633 and 12.633. (Once you round.)