The formula for circumference = 2*Pi*r
R= radius. Radius is half of the diameter, and d= 20. This means that radius = 10. Now we have a full formula to work with.2*Pi*10.
Substitute 3.14 for pi.
3.14 * 10 = 31.4.
31.4*2 = 62.8.
62.8 rounded equals 63.
C = 63.
