Answer:
8
Explanation:
Basically, if the diagonal length is 10, then the hypotenuse is also 10,
Based on the Pythagorean Theorem our equation would be like this..

10 squared is 100 and 6 squared is 36
Now that you know that, set the equation to equal x squared by subtracting 36 from both sides!
100 - 36 = 64
so now the equation looks like this...

To solve for x, find the square root of both sides of the equation
The square root of x squared is x of course. The square root of 64 is 8.
So x = 8 ! :D
Oof that took, so long to type :((