That depends on the terms of then card. What assumptions does your text book make?
She definitely owes 1% (1/12 of 12%) on the previous balance. That would be $11.60.
If the current charges do not accrue interest until the next bill, then they are interest free for this statement. Otherwise, you would need to know what dates these charges were made.
In the case of "no interest now" on current charges, add 518 -83 -270 = 165 to the bill. So. This should mean that 1160 + 11.60 + 165 = $1,336.60 theoretically should pay off the bill IF it were paid on the bill date. Otherwise interest would be charged on the amount owed until the payment date.
The best way to handle this is to make a slight overpayment so that the interest accrued from the bill date until the payment date is covered. A refund will be provided of any excess payment, or used toward subsequent charges.
