Question 66425
Let us consider the two vertices to be the consecutive ones.

(2, -2),  (11, - 10)

Distance between these points = sqrt[(11-2)^2 + (-10 -2)^2]

                              = sqrt[9^2 + 12^2]
                              = sqrt[81 + 144]
                              = sqrt[225]
                              = 15

==> the length of 1 side of the octagon measures 15 units.

Thus the perimeter = 15 * 8
                   = 120 units



Good Luck!!!