[tex]\qquad\qquad\huge\underline{{\sf Answer}}[/tex]
[tex] \textbf{Let's solve for a } [/tex]~
[tex]\qquad \sf \dashrightarrow \:9 + \dfrac{a}{6} = 8[/tex]
[tex]\qquad \sf \dashrightarrow \: \dfrac{a}{6} = 8 - 9[/tex]
[tex]\qquad \sf \dashrightarrow \: \dfrac{a}{6} = - 1[/tex]
[tex]\qquad \sf \dashrightarrow \:a = 6 \times ( - 1)[/tex]
[tex]\qquad \sf \dashrightarrow \:a = - 6[/tex]
I hope you understood the whole procedure ~