The focal distance (focal length) is simply the distance from film plane to pinhole, ergo 3.3125.
The size of the film ultimately has nothing to do with focal length. It does however determine your angle of view, which is dependant upon focal length and film size.
If my math serves me (which is not a guarantee with me...) your aperture is f/331.25
It's possible I'm missing something altogether, but hopefully this helps??