Annette has a credit card that uses the previous balance method. The opening balance of one of her 30-day billing cycles was $2990, but that was her balance for only the first 7 days of the billing cycle, because she then paid off her entire balance and didn't make any new purchases. If her credit card's APR is 31%, which of these expressions could be used to calculate the amount Annette was charged in interest for the billing cycle?

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