Remember when solving problems involving Pi, often it's best to leave the answer in terms of Pi.

When solving for the volume of a sphere, cylinder, cone or solving for the circumference or area of a circle, the answer is typically left in terms of Pi.

If you wish to have a numerical value, you can use the approximation 22/7 for Pi or use 3.14 for Pi.  Of course, if you want more accuracy with your result, you can use more decimal places for Pi. Use as many as you wish.