If you are thinking about buying this book, you are probably teaching yourself Latin with the aid of Latin Prose Composition, and want to see whether your answers are correct. The answer key will not help much. It gives the answer to all of the questions in perfect classical Latin, failing to take into account that the reader probably just wants to know whether his/her translation was grammatically correct. To give an example, the Prose Composition book will occasionally asterisk a word or phrase and tell you to translate it a certain way, and the key will give a completely different answer. It will have you tearing your hair out, thinking your answer to be wrong when it is actually correct, since the key gives one and only one translation to sentences that can be translated a number of ways.
This book is a last resort: if you can, find yourself a teacher.