the coodrinates of JKLM is,
J(1,3) , K(3,1), L(-1,-3) and M(-3,-1)
the length JK is ,
length KL is,
Length LM is,
length MJ
so, the perimeter = sum of sides,
= JK + KL + LM + MJ
= 2 root 2 + 4root2 + 2root2 + 4root2
= 12 root 2
thus, the perimeter is 12 root 2