Answer:
 The $261 Mary deposited before interest was credited .
Explanation:
As given
Mary Moneypenny went to her bank each week and opened a club account. She deposited $21.75 per time period. 
She deposited $21.75 per time period.
If she made 12 deposits before interest was credited.
Than
Mary deposited before interest was credited = 21.75 × 12
 = $ 261 
Therefore the $261 Mary deposited before interest was credited .