It would be 6+6+6+6=24 because you have to add 6, 4 times cuz a recatengale has 4 faces.
C= 2(3.14)r or 3.14D
so, if the diameter (d) is given just multiply it by 3.14. If the radius (r) is given multiply it by 2 then multiply that answer by 3.14 (or just multiply the radius by 6.28)
Pay attention to the units, then find the answer at the bottom.