The right answer is ‘Sixty farthings’.

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A farthing was a quarter of a penny, so 60 farthings would be 15 pennies. The other options are all worth exactly 30. There were four pennies in a groat, twelve pennies in a shilling, and sixty pennies (five shillings) in a crown. In Henry IV Part 2, Falstaff is told that he has seven groats and two pence in his purse, an amusing way of saying 30 pennies.