geometry

So what you'd want to do is find the volume of the sphere, since you're finding out how much paint it can hold. The volume can be found using the equation:

$V = \frac{4}{3} \pi r^3$

So, we're given the diameter. Since d = 2r, we can make that r = (1/2)d to find the radius, which would give us 0.75.

Plugging that into our volume equation gives:

$V = \frac{4}{3} \pi (\frac{3}{4})^3$

We can simplify that down to: 

$V = \frac{9}{16} \pi$

So the paintball holds (9/16)pi units^3 of paint.