In the image I added you can observe that the common endpoint is called a vertex, and<em> the "turn" or aperture formed between the two straight lines (or arms) that converge in the vertex, </em><em>is the angle</em><em> </em>and it can be measured on degrees.
I hope you find this information usefun and interesting! Good luck!
Just replace all of the x’s with 5 and solve using order of operations. I will post what I got for my answer in the comments of the answer if you need it.