The sum of the measures of the interior angles of the polygon in your picture is 540 degrees. I have memorized this fact, but there is a way to figure it out. I will show it down below.
Formula: (n-2) × 180
'n' = # of sides your polygon has
This formula only works for regular polygons like in your case.
5 - 2 × 180
3 × 180
540 degrees
I hope this helps you.
