Answer:
x = +√39
Step-by-step explanation:
In the diagram we see two right triangles. The measure of the base of each one is half of 8, or just 4.
According to the Pythagorean Theorem,
(√54)^2 = 4^2 + x^2, or
54 - 16 = x^2 = 39, so that x = +√39
