To calculate the contestant's balance of prize money after answering 6 questions wrong, we need to multiply the number of wrong answers by the amount lost for each wrong answer.
The contestant loses $12.50 for each wrong answer. With 6 wrong answers, the total loss is:
\[ 6 \text{ wrong answers} \times 12.50 \text{ dollars/wrong answer} = 75.00 \text{ dollars} \]
Since the contestant started with $0 and has lost $75.00, his balance of prize money is:
\[ 0 - 75.00 = -75.00 \]
Therefore, the contestant's balance of prize money is:
B. −$75.00