Imagine a circle, split this circle down the middle. That is your circumference. Now split that line in half too, that is your radius add the number given in your paper next to your diameter same with the radius. Now here is the formula:
pier2 (3.14 X radius X squared) RADIUS
2pie2 (2 X 3.14 X squared) DIAMETER
2r (2 X radius) DIAMETER
draw this out if it helps!!
