we are told that $400 is deposited in a bank account and that every month $200 is added. If "m" is the number of months then the total balance for a given number of months is given by:
[tex]b=400+200m[/tex]In this case, the input variable is the number of months "m" and the output variable is the balance "b". The initial value is $400 and the rate of change is:
[tex]r=200\text{ dollars/month}[/tex]