lookup a code, make a calculation using a number on the codes row

[Guest_imported]

hello.
basically i want to have a button that when pressed will copy a number (the qty) of an item, lookup the code of that item on a different sheet and then subtract the number copied before from the number in the qty column on the sheet:

for example

i have 2 sheets: invoice and price
a1 on invoice will be a product code and b1 a quantity
i want to copy a2 and find the contents of a1 in the a column of the price sheet, and then subtract the number copied from the quantity i.e. bx (x is the row number of the item)
can someone help, thanks

 

[Guest_imported]

i mean:
i have 2 sheets: invoice and price
a1 on invoice will be a product code and b1 a quantity
i want to copy b1 and find the contents of a1 in the a column of the price sheet, and then subtract the number copied from the quantity i.e. bx (x is the row number of the item)
can someone help, thanks

 

[Guest_imported]

anyone?