The line has a slope of 0. It is a horizontal line, where y=-5.5.
Slope is calculated by finding the change in y and placing it over the change in x. For example, two coordinates with a change in y of -3 and a change in x of 2 would be written as -3/2.
In these coordinates, the change in y is 0, and since zero over anything is equal to zero, the slope is zero.
Hope this helped!