Given two points (-7,-5) and (5,-17) you can calculate the slope of the line that passes through them by using the following formula:
Where
m is the slope
(x₁,y₁) are the coordinates of one of the points
(x₂,y₂) are the coordinates of the second point
Then for (-7,-5) and (5,-17), the slope can be calculated as
The slope is m=-1