Answer:
a) $499.20
b) $6,899.20
c) $287.47
Explanation:
First, calculate the interest accumulated in 2 years.
Amount(a): $6400
Interest(i): 3.9% or

years(y): 2
We can say;


Calculate how much he would have to pay per month to fully pay in 2 years.

We can say that,


Therefore, he has to pay at least $287.47/month to pay off in two years.