Bill filed his income tax return with the Canada Revenue Agency (CRA) after the April 30 deadline. He calculated that he owed the CRA $3448, but did not include a payment for this amount when he sent in his tax return. The CRA’s Notice of Assessment indicated agreement with Bill’s tax calculation. It also showed that the balance due was $3827.66, which included a 10% late-filing penalty and interest at 9% p.a. For how many days was Bill charged interest?