auto update of values in rows when rows above is modified

Hi All,
Please refer the attached sample work book, which contains daily sales figures - sales staff wise and channel of invoice wise. What I seek your support is to create a macro or some kind of formula which will auto sum the figures.

Example;
on day 01 Merwin sold 1 unit against DC10 (row 4) and with this sale his Month Till date (MTD) figures reaches 5 (row 6). On date 02nd, he sells 2 units but in DC80 channel (row 14) and the value in row 16 must change to 2 as soon as i press enter from key board. please note that the row 4 to 7 are constant and the position does not change every day. Only the daily values are updated to the daily sales made by the staff.
My look out is that once the value in row 4 & 5 is inserted / updated, their cumulative values in row 6 & 7 must automatically sum up to the day before's value (or subtract if a minus value is inserted, due to sales returns)

Can anyone help, please.

last time one of the distinguished member helped in solving a similar need on "columns" through a vb macro. i am not good in VB and could not find the way to convert that for "rows"

Thank you in advance

I Have created a User defined function for you

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Will sum A1, A6, A11, A16, A21

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Will sum A1, F1, K1, P1, U1

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Will sum A1, A6, A11, A16, A21, F1, F6, F11, F16, F21, K1, K6, K11, K16, K21, P1, P6, P11, P16, P21, U1, U6, U11, U16, U21

Thanks for the help. But this is not solving. The format is only from row 2 to 8. The bottom formats are given for giving you an idea how the format will change on day 2 and 4th. So u have to look only from row 2 to 8:
The figures entered in row 4 gets added in sub ttl row 6 but reduces once it is modified or deleted. The sum value in row 6 and 7 should remain constant to its previous value even if the value on row 4 n 5 is deleted.
Also no change happens in sub total row 7 which should get added up when a figure is entered in row 5.
Can u pls hv a look