To be able to solve this question, we need to know about the Pythagorean theorem: a² + b² = c². A and b represents the two sides that make the right angle, and C represents the hypotenuse, or the longest side, of the triangle.
We know that the hypotenuse is the longest side of the triangle, so that means 9 is c. One side of the triangle is 6, and we have to solve for b. That means 6 is a. We can plug in our values to the formula like this:
Now that we have our equation down, we know what we have to do next: subtract 81 from 36 to get b².