Correct you can tell by splitting them apart. For your first example you have T>S and S>B. the negation of both is /S>/T and /B>/S. which can be connected by /B>/S>/T.

Your second example has A>T and T>/S. The contra of both is /T>/A and S>/T which can be connected by S>/T>/A

Yes thats correct

You asked "How is being a cat sufficient to being a mammal?". Im going to replace the word sufficient with necessary.

How is being a cat necessary to being a mammal? Its not right? I can be a human or a dog and be a mammal. Being a cat is not necessary to being a mammal. But its sufficient. If you are a cat, then its sufficient to say youre a mammal. So think more generally like that question

XD