In A,Z=17 and have equal numbers of protons and neutrons i.e. nucleons=2×17=34
So, for A,
Total binding energy BEA=1.2×34=40.8MeV
Another nucleus B mass number =26
So, total binding energy of B is BEB=1.8×26MeV=46.8MeV
Difference of BE=BEB−BEA=6MeV