In terms of field of view, they will match up along the longest dimension. If you want to look at in terms of a crop factor, and I agree it is often confusing not to mention irrelevant, you take the long dimension of one, and divide it by the other.
I think 6x6 is usually 58x58mm, and 35mm is 36x24mm, so 58/36=1.61. In other words, by that calculation, to get an equivalent field of view to your 80mm lens on 6x6, you'll need a 50mm lens as Steve said.
We never used to worry about these things because until digital came along with a whole raft of different formats (compacts [numerous], 4/3rds, APS-C [various], APS-H, full frame) we only has 35mm to contend with.
6x6 was a completely different animal. It used it's own set of non-compatible lenses and the two never mixed. Not so with full frame digital and crop formats.