create custom auto fill formulas in Excel 2010

My previous experience with Excel is limited to creating worksheets and manually entering data. Today I have learned to create formulas for individual cells and contiguous cells. I have spent most of the day researching and experimenting with creating custom auto fill formulas for a spreadsheet I have been updating manually --- with absolutely no success.

Please see attached file as a sample of what I wish to accomplish. The entries in columns L and M have been created by formulas unique to each cell. My goal is to auto complete columns L and M after each row of data is entered. My problem lies in the fact that the most recent data in columns L and M are not in the same row as my most recent entries. Columns H thru K contain the data to be used in the formulas. My goal is to create two formulas (one each for columns L and M) to perform the appropriate addition/subtraction operations and auto fill these two columns.

Any useful hints or help will be greatly appreciated.

Thanks Ankur,
I tried to copy/paste/drag both formulas from your post to the worksheet with the same results. The formulas were copied down the columns without calculating and entering any values. Did I do something wrong?