Question

Describe a method you could use to find the missing angle

Answer 1

An example would be a triangle.

If you have only 1 of the angles, but 2 are missing, here is a way to solve this.
A triangle ALWAYS adds up to 180. Take the 1 angle, that you do have, and use it to solve for the other 2 missing angles.

This is the same other shapes, everything always adds up to something.
Hope I helped!

Answer 2

You add up all the degrees if it is a parallelogram it needs to add to 360. If it is a triangle 180.