Let us find the circumference of each circle.
The circumference of a circle is given by

Where r is the radius and D is the diameter of the circle.
Circle 1:
Here we are given the diameter of the circle
D = 21 cm
![C=\pi D=(22)/(7)\cdot21=22\cdot3=66\operatorname{cm}]()
So, the circumference of the circle is 66 cm.
Circle 2:
Here we are given the diameter of the circle
D = 91 ft

So, the circumference of the circle is 286 ft.
Circle 3: