OliWW is correct
Jet2 did not fit light weight seats to some of their aircraft to allow them to fly further, but to reduce burn! Any slight increase in range is a secondary function of the first, put it another way they didn't to it to fly an extra 100 miles south of Lanzagroty (clue there's nothing there) if this were a CAA exam, both answer would be correct, but lower fuel burn would be more correct 2 points to OliWW