How to solve for r in: c=k(rr/r-r)

I'll assume you mean      (tell me if i am wrong).first, we can multiply k into the fraction.    we can multiply both sides by  to cancel out the denominator.    distribute c into the left side.    if you want to solve for r, move everything with an r to one side. i will choose left side for this.  then move everything without an r to the other side.so subtracting both sides by krr gets us    adding cr to both sides gets us    factor our r from the left side.    divide both sides by c-kr   

Ac equals 35 cm long