[tex]\bf \cfrac{7y-x}{z}~~ \begin{cases} x=9\\ y=5\\ z=4 \end{cases}\implies \cfrac{7(5)-9}{4}\implies \cfrac{35-9}{4}\implies \cfrac{26}{4}\implies \cfrac{13}{2}\implies 6\frac{1}{2}[/tex]
