Hint, I have an idea, what we should do is to find the length of lines by using the Pythagorean's Theory of a^2+b^2=c^2 since a lot of the incomplete triangle have 2 given side lengths.
There is a theorem in geometry that states that: (8)(8 + 2) = (x)(x)
If you use the other line segment: (4)(4 + 16) = (x)(x)
Either way, you end with: 80 = x2 ---> x = sqrt(80)