Plot the points in the x-y coordinate graph and connect points to form a graph.
Opposite sides of a rectangle are equal so we only need to compute the length of two sides, then multiply by 2 to get the perimeter.
The bottom side connecting points (5,-1) and (12,-1) is of length (12-5) = 7
The left side connecting points (5,-1) and (5,8) is of length (8--1) = 9
the combined length of those two sides is 7 + 9 = 16, thus the perimeter is 16 * 2 = 32.
