Answer 1

One way I've thought of is to enter the formula =ROW() into convenient cells
on rows 5 and 8, say A5 and A8.
Then for your comment enter the formula
=TEXT("Total of rows " & A5 & " to " & A8,)

Answer 2

If you have a formula =SUM(C5:C11) and you insert a row within that range
i.e. 6 - 11, then the formula will change. If you insert a new row 5 or 12
however, the formula will not change.