$\"\"$

Slope of the two non vertical lines is $\"\"$

The y-coordinates are same. So, the line is a horizontal line parallel to x-axis.

Slope of the line is zero.

$\"\"$

Check the solution:

Replace $\"\"$ in slope formula.

$\"\"$

$\"\"$ (Subtract: $\"\"$ )

$\"\"$ (Divide: $\"\"$ )

$\"\"$

Slope is zero.