If we look at the y-axis values of money, we see that they are decreasing. So we can automatically eliminate 2nd and 4th graph (as they are sloping upward).
Also, note that the values are not decreasing at a constant rate. First drop is quite more than 2nd drop and so on. So the graph can't be that of the 1st picture ( as it shows decreasing at constant rate ).
So the correct answer is the 3rd graph.
ANSWER: The third (3rd) graph.
