Explanation:
as a big spoiler : pi is an universal constant. it is the same for every circle, every round object, for circumference, areas, surfaces and volumes.
the formula for a circle circumference :
2×pi×r
the radius is half of the diameter, or the diameter is twice the radius.
so, we have for circle A
pi×9 = 28.26
pi = 28.26/9 = 3.14
and for circle B
pi×5 = 15.7
pi = 15.7/5 = 3.14
the formula for the circle area is
pi×r²
so, for circle A
pi×(9/2)² = 63.585
pi×81/4 = 63.585
pi×81 = 254.34
pi = 254.34/81 = 3.14
for circle B we get
pi×(5/2)² = 19.625
pi×25/4 = 19.625
pi×25 = 78.5
pi = 78.5/25 = 3.14
as mentioned, pi is always the same. it is a natural, universal constant.