The diameter of the plate would be equal to the length of a side of the box.
Find the length of the box by dividing the perimeter by 4:
28 / 4 = 7 inches.
The diameter is 7 inches.
Circumference is found by multiplying the diameter by pi:
The exact circumference is 7PI
Using 3.14 for pi, the decimal answer is:
3.14 x 7 = 21.98 inches ( round answer as needed.)