A line with an equation $$ x = -6 $$ has a slope of _______.

Question Analysis
This question tests the student's understanding of the concept of undefined slope. The equation represents a vertical line, and the slope of a vertical line is undefined.

Key Concept Explanation
The slope of a vertical line is undefined because the change in (denominator in the slope formula) is zero, leading to division by zero.

Step-by-step Solution
1. Identify the given equation: