So, the way to find the slope from points is (y2-y1)/(x2-x1) (x1,y1) and (x2,y2)
So, we'll take the second coordinates, which was (2,3). This means that x2 is 2 and y2 is 3.
The first coordinates are (4,-1), meaning x1 is 4 and y1 is -1. Now lets plug that into our formula
(y2-y1)/(x2-x1) x1=4, y1=-1 x2=2, y2=3
(3-(-1))/(2-(4))
(3+1)/(2-4)
4/-2
-2
So, the slope is -2