Arectangle has vertices (2,0) (5,0), (5,4), (2,4). what is the height of the rectangle?

Each set of numbers in parenthesis can be used to put a point on a grid. So (2,0) would put a point on a grid where x = 2 and y = 0.
x marks where the point lies on the grid horizontally, and y marks vertically.

Using this knowledge, you can see the rectangle if you put it on a grid.
     (2,4)               (5,4)
 
 
 
     (2,0)               (5,0)

Therefore, the height is 5-2, which is 3.