Answer:
4 months
Explanation:
The 24% APR corresponds to a monthly rate of 24%/12 = 2%. This finance charge on a balance of $300 is ...
0.02 × $300 = $6.00
To pay off $300 will take more than 3 payments of $100 because of the finance charge. Because the finance charge is not very large, the last month's payment will not need to be $100, but will be somewhat less.
It will take 4 months to pay off the balance.
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Additional comment
The actual finance charge will depend on your credit agreement. It may amount to $4 the second month, and $2.08 the third month, if it is charged on the outstanding balance. That is, the 4th month's payment may only be $6.08. If there is a finance charge on the initial $300 balance, that may cause the last payment to be a little more than $12.