Answer:
Line 1 negative
Line 2 zero
Line 3 undefined
Line 4 positive
Explanation:
Just like we read words from left to right, look at what the line is doing from left to right.
Positive slope lines are going UP from left to right (Line 4)
The higher the slope the steeper it is. The lower the slope the flatter it is. A line can get flatter and flatter (with a smaller and smaller slope) until its a flat line...
A flat line, a horizontal line (like the horizon) has zero slope (Line 2).
As the slope continues to go even lower-- negative, the line actually goes DOWN from left to right (Line 1)
Vertical lines have undefined slope (Line 3).