Well, I believe the question is asking for Circumference - C. As the question is asking for the amount of ft of monkey grass needed to go Around the circular flower bed.
To solve for Circumference, first solve for the radius variable in the equation.
A = 36 Pi
A = r ^ 2 Pi
R ^2 = 36
R = square root of 36 = 6.
C = 2 Pi R
C = 2 Pi (6)
C = 12 Pi feet.
I believe the correct answer is B. 12 Pi feet.