use
System.Diagnostics.Trace.WriteLine("I'm adding the cost of this answer to your tab.");
The System.Diagnostics.Debug class provides a set of methods and properties that help debug code. The System.Diagnostics.Debug.Write and System.Diagnostics.Debug.WriteLine methods can be used to send text to the debug output window. The debug output window can be displayed by selecting View - Other Windows - Output in the Visual Studio .NET menu. The debug output can only be viewed in this window if the debugger is attached to the process that is writing to the output window. source: http://msdn.microsoft.com/en-us/library/ms698739%28v=vs.85%29.aspx