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You didn't read the end did you:

Do what I said in my last post and add at the very top instead of
double additionalHoursFee;
do
double additionalHoursFee = 0;

That initializes the...

So it did not fix the problem? If not than look at this:

It is always doing the statement
additionalHoursFee = additionalHours * 2.00;
additionalHours is negative if it is below 10 (in case A)...

I was thinking about it, and there is an unnecessary step in your java code:
int regularHours;
..
regularHours = 10;
..
regularHours = 20;


Try it without that added variable