Solve using substitution \[ \begin{array}{c}-x-7 y=15 \\ x+y=-9\end{array} \]

To solve the system of equations using substitution, first solve one of the equations for one variable. Let's take the second equation, \( x + y = -9 \), and express \( x \) in terms of \( y \): \[ x = -9 - y \] Next, substitute this expression for \( x \) into the first equation: \[ -(-9 - y) - 7y = 15 \] Now simplify this equation: \[ 9 + y - 7y = 15 \] \[ 9 - 6y = 15 \] Subtract 9 from both sides: \[ -6y = 6 \] Now, divide by -6: \[ y = -1 \] Now, substitute \( y = -1 \) back into the expression we found earlier for \( x \): \[ x = -9 - (-1) \] \[ x = -9 + 1 \] \[ x = -8 \] Thus, the solution to the system of equations is: \[ \boxed{(-8, -1)} \]