Find last cell in column with sum

I have attached a worksheet for reference. It has some VBA code and worksheet formula. First I import data from a txt file into the DATA sheet. Following I use TRIM macro to reformat the data and enter into DATA2 sheet.
What I need is to be able to find the last data cell in column I and then in the next cell down SUM the column with a single line border above the cell and a double line border below. I also would like to copy the amount from that cell into cell L15. The copied amount will show if there is any difference between that cell and cell L13.

As always thank you for any help offered.

Trevor, you got me man. You rock on the scripting. As always thanks for your help. Frick