(2, 4) (4, 8)
you can sue the formula
y2 - y1 8 - 4 4
--------- = ------------- = ------------- = 4/2 = 2
x2 - x1 4 -2 2
or there's an intuitive way to get it
(2, 4) (4, 8)
look at the y's 4 and 8 whats the space between them ? 4
looks at the x's 2 and 4 whats the space between them ? 2
so its 4/2 or 2