A. The circumference is (pi)d where d is the diameter. So (pi) for circle A is 21.98/7=3.14 and for B is 18.84/6=3.14.
B. Area is (pi)r^2 where r=radius or d/2. So for circle A (pi)=38.465/(3.5)^2=3.14 and circle B (pi)=28.26/(3)^2=3.14.
C. To two places of decimals (pi) has a value of 3.14 in all cases. This indicates or implies that (pi) is a universal constant applying to all circles using the formulae.