r=20in

The circumference of a circle is equal to Pi π times the diameter d.

π⋅(diameter)

Since the diameter d is equal to 2 times the radius r, the formula for circumference using radius is 2πr.

2π⋅(radius)

Substitute the value of the radius r=20 into the formula for the area of a circle. Pi π is approximately equal to 3.14.

2⋅π⋅20

Multiply 20 by 2.

40π in

Find the Circumference circle (20in)