basic sumif function help (urgent)

hey guys,

i need help with a basic sumif function. i have three seperate worksheets, and on the first worksheet i have various months -- which i am trying to calculate total expenses for. on the third worksheet, i have various purchases i made throughout the month.

i am trying to join both details into my first worksheets sums by using a sumif function. i would like the sum of my expenses, increased by the rate of inflation (which i have specified as 2% in an assumptions table beneath the first worksheets main details).

How can I formulate a function for this?

BTW. I have attached the actual workbook for ease of understanding.

Thanks for all your help.