A=(3,0)
B=(0,7)
C=(-3,0)
|AB|=\sqrt{(3-0)^2+(0-7)^2}=\sqrt{3^2+(-7)^2}=\sqrt{9+49}=\sqrt{58}
|BC| = \sqrt{(0-(-3))^2 + (7-0)^2} = \sqrt{3^2+7^2} = \sqrt{9+49} = \sqrt{58}
|AC| = \sqrt{(3-(-3))^2 + (0-0)^2} = \sqrt{6^2} = \sqrt{36} = 6
L=6+\sqrt{58}+\sqrt{58} = 6+2\sqrt{58}