But the question that you have quoted isn't the real question.
If and when you see the real question either method will get you a number that is closer to the CAA answer than it is to any of the other options.
If you plan to move on to the ATPL exams then all I can say is "You aint seen nothing yet". If you get exctly the correct answer in General Nav you should be seriously worried. You have probably done so by accident.