Answer:
D. pi
Step-by-step explanation:
Circumference of a circle = 
Diameter = d
Therefore, ratio of circumference of a circle to its diameter would be:

=> (d cancels d)
Therefore, the ratio of the circumference of a circle to its diameter is 
Commutative property of addition
Just divide 75 by 9 multiplying 100 gives u the answer. And same for the rest
A. 8/$12=21/$x then cross multiply.
B. 1/$1.5