Answer:
The answers are:
Radius: 4.49771869
Diameter: 8.99543738
Step-by-step explanation:
Circumference Formula
C=2πr
28.26=2·π·r
28.26=(6.28318531)·r
28.26/28.26=6.28318531/6.28318531·r
r=4.49771869
d=4.49771869·2
d=8.99543738
Check
C=2πr
28.26=2π(4.49771869)
28.26=(6.28318531)·(4.49771869)
28.26=28.26 ✔
Hope this helps, and I'm sorry if I'm wrong. ;D