Running Monthly Totals

Hi all,

I am attempting to create a worksheet that keeps a tally of monthly totals. Worksheet A is taken from the data in worksheet B. Worksheet A needs to show the current monthly total by month. Worksheet B needs to show the current months activity as shown in cells A1:L7 and to then populate the monthly columns from column N onwards as the amounts change. I am not sure how to sort it so that when i change the amounts in B2:K7 it adds the correct data each month to the monthly columns.

I hope I am making some kind of sense, I attach a copy for you.