[tex]\begin{gathered} -20=8(2f+5) \\ \text{Dividing both sides by 8, we have:} \\ \frac{-20}{8}=2f+5 \\ \Rightarrow\frac{-5}{2}=2f+5 \end{gathered}[/tex][tex]\begin{gathered} \Rightarrow2f+5=\frac{-5}{2} \\ 2f=\frac{-5}{2}-5=\frac{-15}{2} \\ \Rightarrow f=\frac{\frac{-15}{2}}{2}=\frac{-15}{4}=-3\frac{3}{4} \end{gathered}[/tex]
