It is very simple to calculate slope of a when you have two pair of points. You can use the following formula.
M=(y2-y1)/(x2-x1)
Here the two points are
(8,-1) and (4,3)
so
m =(3+1)/(4-8)
m=4/-4
m=-1 is the required slope of the line.
M=(y2-y1)/(x2-x1)
Here the two points are
(8,-1) and (4,3)
so
m =(3+1)/(4-8)
m=4/-4
m=-1 is the required slope of the line.