I DONT UNDERSTAND THIS PLEASE

Answer:
D. undefined
General Formulas and Concepts:
Algebra I
Step-by-step explanation:
A horizontal line has a slope of 0.
A vertical line has a undefined slope.
Any other line will have a slope of some number.
Answer:
D
Step-by-step explanation:
The slope of a line represents the number of units a line rises or falls vertically for each unit of horizontal change from left to right.
1) A line with positive slope (m > 0) rises from left to right.
2) A line with negative slope (m < 0) falls from left to right.
3) A line with zero slope is horizontal (parallel to x-axis).
4) A line with undefined slope is vertical (parallel to y-axis).
Ans: The line is parallel to y-axis. So, the slope is undefined