Eliza started her savings account with $100. Each month she deposits $25 into her account. Determine the average rate of change in Eliza's account from the 2nd month to the 10th month. Show all work for full credit.

"Each month she deposits $25 into her account" tells me that the average rate of change from the 2nd to the 10th month is simply $25/month.  Of course you can calculate this using the "average rate of change formula"
   
                             f(b) - f(a)
ave r of c = ---------------------
                       b - a

Here f(x) = $100 + ($25)x, a = 2 and b = 10