the main condition can be found one of the following given methods:
if A = B*C*D, if we want to find the value of B, so B = A /C*D, the similar method can be applied to find the value of C an D. These are C= A/ B*D and D = A /C*B
in our case we have C = 2*Pi* R,
solve for R does mean, searching the value of R, so
if we want to find the value of R,
it is R = C / 2*Pi
