Macro With Formulas - Subtracting Next Order With Current Stock

I would like to use this database list I export from another program to excel format. What I want to do is to change in the C column.

The value under Akt.saldo is how much of a given article we have in stock (saldo). And the Rest. in column B is the reservation, how much of that article thats is going to be shipped at that day. ex 14161 year(14) week(16) day(1).

So as you can see in column C the Rest. value never subtracts from the stock. What is want is something like that below.

Here is just selected all the values under stock and moved to the next column. Then used white color to hide it.

Here i subtract the hidden value with the reservation to be able to see how much is left after that order.

And the same here. Subtracting next order with the current stock.

How do i do this with a macro? The list is changing everyday.