Hello there!
First, let's take a look at our equation.

- 15 = 34
We need to isolate x^2 to completely square root both sides properly, so let's do so.
Add 15 to both sides to isolate

.
We are now left with:

= 49
Now, square root both sides.

= x

= 7
We are now left with the solution:
x = 7
I hope this helps!