Help Determining Focal Distance

Hello Everyone,

I am trying to figure out the focal distance of my new pinhole conversion camera and I'm a little confused. I've tried the wizards to help me figure this out but I'm still a little lost. I think the grey area is determining the film dimensions. So If im shooting 120 film on a 6x9 frame is my film dimension going to be 90mm?

Here are my dimensions...Anyone bored enough to calculate this for me?

Pinhole to film plane distance = 3 5/16 inches

Pinhole Diameter = .010 inches

Film Dimensions = 6x9 cm

Thanks to anyone who can help me out here :p