Solution
We are given the equation
[tex]y=9-3x[/tex]We want to find y when x = -3. We only need to put x = -3
[tex]\begin{gathered} y=9-3x \\ y=9-3(-3) \\ y=9+9 \\ y=18 \end{gathered}[/tex]Therefore, the answer is
[tex]\begin{equation*} 18 \end{equation*}[/tex]