The answer is

In the choices; the coefficients 21, 32 and 10 are not perfect squares.
54 muffins because if you take both your given fraction find the nearest common denominator which is 3 4/12 divide the 4 and 12 to get 3 than divide by 0.10 than divided by a whole 10 which got me 3.03 etc.
Round it see how many times it can go into 10 3 times than multiply it by 18.
C=Pi X D
Diameter is twice the radius so that would be 24 feet
C = Pi X 24
C = (22/7) X 24
C = 75.428 Feet.