Wanting to create an automated calculator

What you're asking for is fairly simple. However, knowing how it would fit in to your workbook, where it would fit in...i.e., how your workbook/spreadsheet is organized beyond what you show in the image, is both important and not at all clear from the image. Would it be possible for you to share an entire workbook?

Are the three codes you show the only ones? How are they entered? By whom?

As is often the case with Excel, there would be several different ways to resolve this kind of situation, several different ways to write formulas, several different ways to minimize laborious entry tasks. Rather than just give you a simple formula [e.g., =IF(code=2899,base_sal*1.2,base_sal) ] it really would help us help you if you described who is entering the start and finish times, whether you expect the computer to calculate how many hours were worked and determine what code applies, or will whoever enters this data also be entering the relevant code?