What is the length of x in the diagram below? (picture below)

The triangle on the right side is a 30-60-90 right triangle.
This type of right triangle has special rules for finding the sides and hypotenuse.
hyp = 2 * short leg
long leg = sqrt3 * short leg

From the triangle on the left, 45-45-90 right triangle, we get that the height is 5. This becomes the short leg of the triangle on the right. To find x, the hypotenuse just multiply the short leg(5) by 2.
Hyp = 10