BPP kit -Q106

The answer to part c is 26,477 (27,630+4,085-5,238) ,on page 159.

When computing before, we took off 15% from leasing charges so why is this not taken into consideration when assessing the benefit, which would mean:
22,333 (23,486+4,085-5,238). Making this more beneficial than director’s remuneration alternative.

Thanks for having a look