Well the line is straight so it will always have the same slope no matter what points you use but to solve it mathematically you do change in y/change in x
(3.5-(-1))/(4-(-5)) 4.5/9 = 0.5 So the slope is 0.5
Now pick 2 random points on the line (-3,0) and (5,4) Now do the same thing for these 2 points