Answer:
8
Explanation:
There are two ways to solve this!
1. Use the Pythagorean Theorem
a^2 + b^2 = c^2
6^2 + b^2 = 10^2
100 - 36 = b^2
64 = b^2
8 = b
2. Shortcut using 3-4-5 triangles
A 3-4-5 triangle has to do with the ratios of each side.
In this case, it's 6-8-10, as each number is multiplied by two with the same 3-4-5 ratio. This is a good shortcut for these types of problems and will be handy on tests like the SAT as well! :)