I wish i could show u how to work it out but just do it or work it out the same way as the fractional numbers.
Answer:

Step-by-step explanation:
Draw a diagonal (line segment from one corner to the opposite corner). You'll form two right triangles with the diagonal being the hypotenuse of both triangles.
Use the Pythagorean Theorem: (leg)^2 + (leg)^2 = (hypotenuse)^2.
Let h represent the length of the hypotenuse.

The question is just a bit vague. It should say opposite corners. I'm assuming the question does not mean the length of one side!
I honestly don’t understand
8 - 3x - x = 12
8 - 2x = 12
-2x = 12 - 8
-2x = 4
x = -2