how to edit data first column and then after

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VB6

Hi all, I have a ms access table data as bellow
slno stockid stock value
1 4062 120 10
2 4062 100 11
3 4062 300 13

I want to deduct the stock from this table using an input quantity.Some times quantity is more than the stock available in this row have to go to next column and it will deduct the stock in that row.please how to create the code in vb.The advantage of this method if I input 150 first it will deduct 120*10 and 30*11

Thanks