Your method and answer are correct Wings of fire.
But your comment that
Now drift = angular difference between track and heading
Is true when discussing drift in the normal sense, but this question isn't really about drift. I think that the examiner put in the words "constant drift" just to eliminate any unwanted complications. It would probably have been better to have said "in nil wind conditions".
The difference between the Great Circle track and the Rhumb Line track isn't realy an example of drift. At the start of this leg when the heading is 274.145, the track will also be 274.145 (assuming nil wind). And at the end of the leg when the heading was 265.855 the track will also be 265.855. But the average track over the whole leg would have been 270.