The formula to calculate de perimeter of a rectangle is :
(Width x 2) + (Length x 2) = Perimeter
Width = 6 2/3
Length = 2 x (6 2/3) = 13 1/3
Replace your values in the formula and calculate everything to find the perimeter :
(2 x (6 2/3)) + (2 x (13 1/3)) = Perimeter
13 1/3 + 26 2/3 = Perimeter
13 + 26 = 39
1/3 + 2/3 = 1
39 + 1 = 40
40 = Perimeter
There you go! I really hope this helped, if there's anything just let me know! :)