The area of the circle is found by multiplying the value of PI by the radius raised to the power of 2
the circumference of a circle can be found in 2 ways. If you know the diameter of the circle multiply that by the value of PI. If the radius of the circle is known multiply that by 2 then multiply that by the value of PI.
The information needed is what value of PI to use and either the radius or diameter of the circle.
The circumference is the distance around the circle , so you would want to know the circumference to determine the number of rotations a tire makes.
