Geometry

Question Analysis:
This question focuses on the properties of a triangle, specifically using the angle - angle - side relationship to determine the side length.
The main idea is to recognize the type of triangle based on the given angles and then use the property of that triangle type to find the unknown side length.

Key Concept Explanation:
- Equilateral Triangle Definition: A triangle with all three angles equal is an equilateral triangle.
In an equilateral triangle, all three sides are of equal length.

Step - by - Step Solution:
1. First, find the measure of .
Since the sum of the interior angles of a triangle is , and , , then .
2. Since