You could use distance formula three times to calculate the length of each side. Add the three lengths to find the perimeter. However, (see image) if you look at a graph of these points, two of the sides are the hypotenuse of a right triangle that have known, integer values--Pythagorean triples. The sides are 3-4-5 and the other is 6-8-10. We use the Pythagorean theorem to find the third side. See image.