The first thing he has to do is take that "minus" sign through the parentheses containing the second polynomial. Some students find it helpful to put a " 1 " in front of the parentheses, to help them keep track of the minus sign. Here's what the subtraction looks like, when working horizontally.
100 dollars should be a one time fee so that has to be added to the equation, and since it is a one time fee it should not have a variable next to it.
It also says that you have to pay 720 dollars per month, so it has to have a variable next to it to show the number of months that she needs to pay that amount of money.
The answer should be D.
y= 720x +100
The average rate of change is the change in y divided by the change in x...
(f(8)-f(4))/(8-4)
(4-12)/4
-8/4
-2
So the average rate of change is -2.
