Degree of Operating Leverage

how did the formula for DOL = % change in EBIT/ % change in Sales become = Q(P-V)/Q(P-V)-F

I dodnt understand the derivation ???

pg86 Schwezer

Thnx in advance

I wrote an article on this that may be of some help here: http://financialexamhelp123.com/degree-of-operating-leverage-dol/