the formula for circumstance of a circle is:
C= 2×pi×r or C= pi×d (the diameter actually consists of 2 radiuses)
1.
C= pi×7
≈21.99
2.
C= 2×pi×9
=18×pi
≈56.55
3.
C= 2×pi×5
=10×pi
≈31.42
