Answer:
8.9
Explanation:
There are no letters to define this properly, but the hypotenuse of the triangle with the sides 2 and 4 is = √(2²+4²) = √20 (pythagorean theorem)
Now we can find x, using pythagorean theorem again.
√20²+ x² = 10²
100 - 20 = x²
x = √80 = 4√5 ≈ 8.9
Cheers!