We have the following:
Since they vary directly, it means that they are directly proportional, therefore
[tex]\begin{gathered} x=4\rightarrow y=-8 \\ x=-4\rightarrow y=? \end{gathered}[/tex]
solving:
[tex]\begin{gathered} y=mx \\ \text{replacing} \\ -8=m\cdot4 \\ m=\frac{-8}{4} \\ m=-2 \end{gathered}[/tex]
now, replacing
[tex]y=-2\cdot-4=8[/tex]
Therefore, the answe is 8
