Answer:
That is a 45-45-90 triangle next to a 30-60-90 triangle.
So, the height of the left triangle equals 5.
That makes the short side of the 30-60-90 triangle also equal to 5.
In a 30-60-90 triangle, the hypotenuse (or "x") is exactly twice the length of the shortest side.
Therefore, the hypotenuse (or "x") equals 10.
Explanation: