Question

The diagram shows a convex polygon what is the value of z?

Answer 1

When you have unknown, or missing angles, you need to take the two given angles and add them together. 

31° + 100° = 131°

After you added those together, you need to subtract the sum from 180°. Why do you only subtract 180°? Well, every angle or figure has 180°, nothing more.

180° - 131° = 49°

So, z = 49°

I hope I helped :)