Prorata Calculations

Dear Sir,
Anybody can help me for the following problem
Consider 2 work sheets containing
One sheet Budgeted figures from April to March
Another sheet Actual figures for the same months and one column extra for showing budgeted figure (on Prorata basis)
suppose if I enter the actual figure for April the budgeted figure up to april
If I enter the may actual figure then in the same budgeted cell it should sum the april and may budgeted figures of 1st sheet and should display.
Like wise if i enter the December actual figure the Prorate budgeted cell should calculate the sum of April to Dec. budgeted figures of 1st sheet and display the figure.
Regards
Murali

Dear Sir,
There is an error when I am up loading the excel file itself

Dear Sir,
The upload manager is some problem it seems kindly look into the image file and do the needful.
Regards
Murali