To solve this question, you need to know the rate in which the money is being spent. First, you know the y-intercept, which is 4000, or the money she owned before spending it. Next, you know, how much she had spent in the duration of 3 months. So, if you substitute those numbers into y=ax+b, it would be 2800=-3a+4000 (or 2800=4000-3a either way it is equivalent) If you solve this, you know that the college freshman is spending her money at a rate of $400 per month. Hope this helps :)
