In the HL theorem, the hypotenuse and one length of the two triangles are equivalent. In order to calculate the value of x, we equate the two values of the hypotenuse:
2x + 9 = 4x - 1
2x = 10
x = 5
With x = 5, the hypotenuse of SUV works out to be 19, and the hypotenuse of WUT also works out to be 19.