Statements: (a) All frogs are tortoises. (b) No tortoise is a crocodile. Conclusions: I. No crocodile is a frog. II. No frog is a crocodile.

First Premise is Universal Affirmative (A-type).
Second Premise is Universal Negative (E-type).
All frogs are tortoises. ↔ No tortoise is a crocodile.
A + E ⇒ E-type of Conclusion "No frog is a crocodile".
This is Conclusion II.
Conclusion I is Converse of this Conclusion.