Even if you treat it as a real question, it's not that hard, because buses meet maximum vehicle width restrictions, are of a few common lengths (which are rarely violated because they want to meet CDL gross vehicle weight restrictions so normal bus drivers can drive them), and the interiors are basically standardized.

Using 35' x 7.5' x 6.5' would give you a reasonably close interior volume.

Golf balls, on the other hand, have a standard volume (2.483 cubic inches). Even if you didn't know the number, you could guess pretty well and say the radius was an inch (which would get you close).

Even if you start varying the bus width, length, and height, you can see the answer is somewhere between 1 and 2 million for a sanely sized bus.