Can you insert sub-total cells which vary controlled from dropbox

[BIGTREV]

I need to insert various sub-totals in a column which sums the cells immediately above it but want to do this from a dropbox (or other simple method) which is in a remote column/cell.

i.e., the attached shows various sub-totals in the same column which sum the cells immediately above but only within the sub-section it belongs to. You will note that each section has a different number of rows that it has to sum.

To overwrite each cell to carry out the function is obviously very time consuming which is why I need an automatic solution.

I would like to be able to use a dropbox that would sit in another column which would automatically tell the relevant cell to change state and sum the cells between it and the next sub-total directly above and in the same column.

If I the revert the dropbox back again, I want the cell containing the sub-total to reset back to its original state.

Can this be done?

Regards.