He will need to make 6 more payments in order to ensure that the outstanding balance becomes 0.
When there is an ongoing repayment schedule for a credit, there is a time-frame expected for full repayment which is calculated with an interest rate to ensure the balance equals zero.
Here, the observation shows the balance reduces by $100 every months, thus, the balance of $615.70 is expected to be fully paid in 6 months ($101 * 6 months).
Therefore, the Option C is correct.
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