1. **State the problem:** Solve the system of equations by substitution: $$y = -x$$ $$y = -3x - 16$$ 2. **Use substitution method:** Since both expressions equal $y$, set them equal to each other: $$-x = -3x - 16$$ 3. **Solve for $x$:** Add $3x$ to both sides: $$-x + 3x = -3x - 16 + 3x$$ $$\cancel{-x} + 3x = \cancel{-3x} - 16$$ $$2x = -16$$ 4. **Divide both sides by 2:** $$\frac{2x}{\cancel{2}} = \frac{-16}{\cancel{2}}$$ $$x = -8$$ 5. **Substitute $x = -8$ back into $y = -x$ to find $y$:** $$y = -(-8) = 8$$ 6. **Final solution:** $$(x, y) = (-8, 8)$$