Hi welcome to OCC!
The one on the right I think you mean QA-42, the one on the left looks like a QA-42A. The QA stands for quick attach, which your tractor does not have. No worry because it also has bolt holes that you would use to mount it on your 100. You can look it up like I did on partstree.com, put in "cub cadet 100 garden tractor" and it will come up on the list of possible matches. Then scroll down the parts breakdown list to the compatable attachments section, both are listed.
On a personal note, I think a 42" thrower is a bit much for 10 hp. If it were mine, I would get a 36" thrower. I'm sure someone will follow up saying they used a 42" on a 10hp for years....your machine, your call.
Bill