It is because the formula for the circumference of a circle is 2 x 3.14 x r so I do the 2 x 3.14 and I get the 6.28 and then 6.28 x 3.5(radius) is 21.98.
Try plugging them in, might seem tedious, but it's the best way to practice. if you plug in a pair and the left side of the equation is less than or equal to 6, it's the right answer.
