Given question:
[tex]\begin{gathered} 3x-7y=9 \\ x=-2 \end{gathered}[/tex]To find the value of y, we will follow the steps below
Step 1: make y the subject of the formula
[tex]\begin{gathered} 3x-7y=9 \\ 7y=3x-9 \end{gathered}[/tex]Step 2: substitute the value of x=-2 into the expression above
[tex]\begin{gathered} 7y=3(-2)-9 \\ 7y=-6-9 \\ 7y=-15 \end{gathered}[/tex]Step 3: Divide both sides by 7
[tex]\begin{gathered} \frac{7y}{7}=-\frac{15}{7} \\ \\ y=-\frac{15}{7} \end{gathered}[/tex]Thus, the value of y is:
[tex]-\frac{15}{7}[/tex]