The solution for the mock exam in the book is given in the book.
The mock exam simulator that can be downloaded, intentionally does not divulge the answers, like the real exam.
This is a feature of the mock exam simulator.
I agree with you that ideally the exam simulator ought to show the answers.
This exam simulator is basically the same as the one that was released with the second edition of the book.
We basically upgraded it with questions for SCJP 6.
We are talking with JavaBlackBelt (http://www.javablackbelt.com/) to make the mock exam available online, which we hope will provide a better learning experience.
So watch the book website for the annoucement.