Points on a plane has two coordinates (x, y). The x-coordinate refers to x-axis, the y-coordinate refers to y-axis.
Using the distance formula, the distance between points E and F is:

Similarly, the distance between points E and G is:

The distance between points F and G is easily seen in the graph, d = 7.
Finally, the perimeter of the polygon is√8 + √29 + 7 = 15.2