Summing with Dynamic Data

I am sure most of you macro whizzes know the answer to this one, but since i am basic I kindly ask assistance.

My situation is I am trying to create a macro to that will give me the sum of columns G-AF. I need to get the summary for 3 subtotal lines and one grand total line of which the rows are dynamic and will change each day.

'Line Total 1' should be a summary from row 3 to the row directly above it.
'Line Total 2' should be a summary of the first row below where 'Line Total 1' ends to the first row above 'Line Total 2'
'Line Total 3' should be a summary of the first row below where 'Line Total 2' ends to the first row above 'Line Total 3'
'Grand Total' should be a summary of 'Line Total 1' + 'Line Total 2' + 'Line Total 3'.

Any help would be greatly appreciated.