So, make it easier.
If you knew the area of a square was 36 sq. inches, and had to find the length of the sides, the first thing to remember is what you know about squares.
Squares have sides with equal side lengths.
Then you would think since the sides are the same length and one side is marked "x"... x times x must equal 36.
x^2 = 36
Take the square root of each side
You will use the same thinking for your problem.
2x times 2x equals 34 square inches