If I'm correct, Behringer 180 is a bass combo, Crate 100 is a guitar head .. why would you like too hooke these two?
But if you really want to do it, you would have to find the wire in Behringer that goes from amp to speaker and uplug it (or cut and solder on a connector). Than you only have to conect Crate head and Behringer speaker with a speaker cable.
But I still don't see any sense in it. It won't get any louder or something like that...