Displaying values neatly in C++ using a exercise.

I want to find out how to use decimals as a multiplication metric inside of the coding. Edit: Went back to try multiplying by .4 and .2 again and IT WORKED!!! I also figured since we're working with money it's best to use double instead of int for decimal place holders. I also added dollar signs inside of the print liens in order to showcase that this is money I am talking about. Edit 2: I didn't utilize constants at all in my coding. I still don't quite understand their usage. I know that they keep you from changing what the value is set to afterward but I can't think of any case that's applicable.