Jessica plots the data points relating the amount of money she needs to repay a loan and the number of months she has been making payments

The data points shown are the black dots on the plot. From the graph, it is obvious that the data points fit more on the linear model than the exponential model. To illustrate this clearly, let's find the difference of consecutive data starting from the 12th month:

2,110 - 1500 = 610
1,500 - 870 = 630
870 - 220 = 650

Hence, it shows that more or less, the trend decreases about the same amount every 6 months. The answer is A.