Concept:The sum of the interior angles of an n-sided polygon is given by (n−2)×180∘.Explanation:Let n be the number of sides of the regular polygon.The given sum of interior angles is 540∘.Using the formula: (n−2)×180∘=540∘.Divide both sides by 180∘ to get:n−2=180∘540∘=3.Add 2 to both sides:n=3+2=5.So, the regular polygon has 5 sides.Answer:C. 5