Geometry

Question Analysis:
This question is centered around the property of the interior angles of an equilateral triangle.
The main focus is to utilize the fact that each interior angle of an equilateral triangle has a fixed measure to establish an equation and solve for the variable .

Key Concept Explanation:
An equilateral triangle has the characteristic that all three of its interior angles are equal, and each interior angle measures .
This is a fundamental and well - known property in the study of equilateral triangles.

Step - by - Step Solution:
1. Since each interior angle of an equilateral triangle is , and the given angle is , we can set up the equation:
  - .
2. Subtract 2 from both sides of the equation:
  - , which simplifies to