Formula to subtract 7th column values from the column before the 1st (loop)

I have a code that inserts a new column after every 7th column. I want to include a formula where every 7th column value is subtracted from the values present in the column before the 1st, or you can think of it as subtracting 7th column of the present group from the 7th column of the previous group. Example: The range of my data starts from col F, then

F (7th) New Column (G) H (1st) I (2nd) J (3rd) K (4th) L (5th) M (6th) N (7th) New Column (O) P (1st) Q (2nd) R (3rd)

So, New Column (O) = N - F
and the next New Column (W) = V-N ...

NOTE: Column G can be ignored.

I want to add a looping function to this so that it will continue to subtract for the other respective columns as well.

How do I incorporate this into the following code?

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P.S. I'm using Excel 2013 and I'm a beginner at this so any help would be much appreciated!

Just reverse it.....

Change this

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To

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Thanks for your reply

Although that wasn't exactly what I was looking for. But I actually found another way around it. I filled up the blanks cells in columns with 0. Then used the insert columns macro as specified in my original post. Then used the Go To Special option to select only the blank cells which in this case would now only be the new columns. I typed the subtract formula, clicked Ctrl and tapped Enter. This copied the formula down all the respective new columns. ^^

Now I need to see how I can select and delete the columns at specific intervals..