Algebra Help? PLEASE.. THANKS?

Question

Solve C= 2ttr for r. (tt = Pi) Then find the radius of a circle with a circumference of 15tt (tt = Pi)

Answer 1

Since the r is multiplied by 2π, you will do the opposite, divide by 2π.

So r = C / (2π)

Then you'd have r = 15π over 2π.  The πs cancel leaving 15/2 or 7.5

Answer 2

15p = 2pr

7.5 = r  

Answer 3

c = 2(pi ) r

c/(2pi)= r

15Pi / 2pi = r

7.5 = r