Okay, since she started with $100, then that would be a constant. So the function would start off with f(x)=?+100. Okay, now since she is depositing $25 PER month, then the 'x' varibale would be per month. So the function would be f(x)=25x+100. Now since you want to know the rate of change, just insert the x value as the month. For example, you want to know how much money she has on the 4th month, so you would substitute 4 with x --> f(x)=25(4)+100, which is f(x)=200
