If you know the answer, SOLVE THE PUZZLE! The higher your score, the more likely you'll spin a Bankrupt. Thus it's prudent to finish puzzles as quickly as possible.
Press the menu button during the bonus round. The timer will stop, giving you more time to solve the puzzle.
When guessing, remember that the most common letters in the English language are E, T, A, O, N, I, R, and S.