Hello from MrBillDoesMath!
Answer:
r = C/6.28
Discussion:
Note that C = 2 * Pi * r is the exact formula. As Pi is approximately 3.14, the given formula, C = 2 (3.14) r, is an approximation. Solving it for r:
C = 2(3.14) r => as 2 * 3.14 = 6.28
C = 6.28 r => divide both sides by 6.28
r ( 6.28/6.28) = C/6.28 => as 6.28/6.28 = 1
r = C/6.28
Thank you,
MrB