that depends on what magnification you want to shoot at. shooting at infinity will produce a different focal length equivalent than shooting up close, say a frame filling portrait. for infinity it's just straight ratio of format diagonal lengths. for up close, then the bellows extension becomes significant and it will put you in the "macro zone" with the 4x5, which will result in a much longer equivalent focus than the infinity focus.
so 4x5 diagonal = 6.40" and 2.25" diagonal = 3.18"...at infinity then this is equivalent to shooting a (3.18/6.40)*17" = 8.45" = 215mm. up close though it can be equal to a LONGER lens depending on how close you want to focus. If we know the length of the tube, we can figure out the total bellows draw that is possible on your camera and give you that length--closest focus. since that thing don't look like 17" long, I"m thinking that with the bellows almost all the way out, plust that tube, you'd get infinity focus---that is--it wouldnt' be a closeuplens...but I'm just going by looks here....don't know the actual dimensions.