x is approximately 62.23 units
Separate the square into two right triangles. Since all 4 sides of the square are congruent (equal to each other), they are all 44 units long. The Pythagorean Theorem is a^2 + b^2 = c^2, where a and b are sides of the triangle and c is the hypotenuse (longest side of the right triangle, in this case would be x).
44^2 + 44^2 = c^2
1936 + 1936 = c^2
3872 = c^2
Take the square root of both sides.
c is about 62.23
c = x, so x is around 62.23 units long
Hope this helps