Final answer:
The diameter of a circular pool with a radius of 9 feet is 18 feet, which is twice the radius.
Step-by-step explanation:
The diameter of a circular swimming pool with a radius of 9 feet would be twice the radius. Therefore, to calculate the diameter, you multiply the radius by 2.
Diameter = 2 x Radius
Diameter = 2 x 9 feet
Diameter = 18 feet
The correct answer is option b) 18.