Answer:
x = 9/2
Explanation:
The outside triangle is also a right triangle, with hypotenuse 8 and side 6.
The missing side can be calculated with pythagoras as:
Now for the vertical line, lets call it y, which is a side for two "back to back" triangles, you can do pythagoras twice:
left triangle:
right triangle:
Eliminating y², you can solve: