Absolute Cell Referencing

I need to work out a total of column A7:A39. Even with my lack of excel knowledge, I can do that with the sum formula. But, each week, I need to delete the values in A39 by deleting that row, and inserting a row into A7 and putting different data in.

I have my $ signs in place to make sure the formula relates to that column only, but when I insert the row at A7, the formula moves to A8:A39 not A7:A39.

Basically I need to be able to delete and insert but still be able to view the sum of A7:A39 at all times. Any ideas how?

... or the non-volatile equivalent, =SUM(INDEX(A:A, 7):INDEX(A:A, 39))

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