Cell calculation - Text query ( Add / Subtract depending on text )

Hi,

Very basic knowledge of excel.

I have created a spreadsheet to accrue and take hours from my employees.

I have a drop down list that can be selected as either taken or accrued. I am trying to find a simple formula that depending on whether that cell reads taken or accrued it will either add or minus the hours from the balance cell...???

Any help would be much appreciated.

Dan