To calculate the additional interest paid, we first need to understand how interest is charged.
For a credit card, if the statement balance isn't paid in full by the due date, interest is typically calculated daily on the average daily balance for that billing cycle. The grace period is the time between the end of a billing cycle and the due date for that bill; during this time, no interest is charged if the bill is paid in full by the due date.
In this case, the subscriber pays off part of the balance in the first three months and then the rest at the end of the fourth month.
Let's calculate the interest:
First, convert the annual percentage rate (APR) to a daily rate:
23.99% per year = 23.99 / 365 = 0.0657534% per day
Month 1:
Beginning balance: $99.99
Payment: $15
Balance after payment: $99.99 - $15 = $84.99
Interest for the month: $84.99 * (0.0657534/100) * 30 = $1.67
Month 2:
Beginning balance: $84.99 + $1.67 = $86.66
Payment: $15
Balance after payment: $86.66 - $15 = $71.66
Interest for the month: $71.66 * (0.0657534/100) * 30 = $1.41
Month 3:
Beginning balance: $71.66 + $1.41 = $73.07
Payment: $15
Balance after payment: $73.07 - $15 = $58.07
Interest for the month: $58.07 * (0.0657534/100) * 30 = $1.14
Month 4:
Beginning balance: $58.07 + $1.14 = $59.21
Interest for the month: $59.21 * (0.0657534/100) * 30 = $1.16
Total Interest Paid: $1.67 + $1.41 + $1.14 + $1.16 = $5.38
If the subscriber had paid off the balance during the grace period, no interest would have been charged. Therefore, the additional interest paid is $5.38. However, this option isn't given among the provided choices. Please double-check the problem or options.