First we pass the -18 to the other side, like this: [tex]y + 18 = x^{2} [/tex].
Then we change sides, like this: [tex] x^{2} = y + 18[/tex].
And at last, we put a square root, like this: [tex]x = \sqrt{y+18} [/tex].
So the answer is: [tex]x = \sqrt{y+18} [/tex].
Hope this helped! c: