Ok Keith, thanks again, I have redone the exercises and I know now what went wrong.
Firstval, for Q1 everything is ok if I reduce the total mass to take into account for the reduced passenger numbers.
Next, for Q2 none of the proposed answer works. Thus I consider it to be an error from the question bank or from JAA.
Last, for Q3, I was misinterpreting the exercise. I got it now. Thanks.
Have a good day,
Emmanuel.