Answer:
57.07 months.
Joseph must decide whether the 57th payment was $1,327, or he can pay a 58th payment of just $92.
Explanation:
The easiest way to calculate a monthly payment is using a payment calculator:
Monthly payments = $1,185.04
Since Joseph will pay an extra $50 each month, his payment = $1,235.04
By paying that extra amount Joseph will reduce his payments by almost 3 months to 57.07 months
After the 57th payment, Joseph' balance = $91.43, so he can decide to pay a little on the 57th payment or just pay $92 next month.