Answer:
540°
Step-by-step explanation:
Consider a regular pentagon. Divide it radially into five congruent, isosceles triangles. Each triangle has a vertex angle of 360°/5 = 72°, and base angles of (180°-72°)/2 = 54° each.
An interior angle of the pentagon is made up of two of those 54° angles, so interior angle = 108°.
Sum of interior angles = 5·108° = 540°
