We can use an approximation of pi. pi = 3.14.
sqrt(16)/4 = 4/4 = 1
2pi = 2 * 3.14 = 6.28
We need to find the number that is not between 1 and 6.28.
A pi = 3.14; 3.14 is between 1 and 6.28, so this is not the answer.
B sqrt(9) = 3; 3 is between 1 and 6.28, so this is not the answer.
C pi/9 = 3.14/9 = 0.349; 0.349 is not between 1 and 6.28, so this is the answer.
D pi^2/9 = (3.14 * 3.14)/9 = 9.86/9 = 1.095; 1.095 is between 1 and 6.28, so this is not the answer.
Answer: C pi/9