To solve for the circumference and the area of a circle, first you must determine the radius.
D = 21 inches
R = 1/2D = 1/2(21) = 10.5 inches.
C = 2pi • r
C = 2(3.14) • 10.5 inches
C = 65.97 inches.
A = Pi • r ^2
A = (3.14) • 10.5^2
A = 346.185 in^2.
The area of a circle is 346.185 in^2.