Calculating total depending on kind of transaction

Hi all, I am looking for some help with calculating the totals depending on kind of transaction. In attached example: Col B is setting the kind of transaction, Col C is change quantity and Col D is what I am trying to work out. Whenever transaction is BOM Issue, Out - POP or Out - Write off, I need the formula to subtract the value shown in Col C from Col D but when transaction is In - POP, In - Unknown source or In - Internal return, I need the formula to add value from Col C to Col D. Other transaction do not matter in this formula and need to be ignored. Can you help please?

Hi cubangt, thanks for this. My aim is to calculate the results shown as example in column D. Raw data I get is column A,B and C so need a formula to calculate the qty at time of the transaction so effectively it will always start from 0 and then calculations will affect it as listed. Do you think it can be done?