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.
