1. **State the problem:** Solve the system of equations: $$-y = x$$ $$-3x + 3y = -36$$ 2. **Rewrite the first equation:** From the first equation, multiply both sides by $-1$ to isolate $y$: $$-y = x \implies \cancel{-}y = \cancel{-}x \implies y = -x$$ 3. **Substitute $y = -x$ into the second equation:** $$-3x + 3(-x) = -36$$ 4. **Simplify the equation:** $$-3x - 3x = -36$$ $$-6x = -36$$ 5. **Solve for $x$:** Divide both sides by $-6$: $$\frac{-6x}{\cancel{-6}} = \frac{-36}{\cancel{-6}} \implies x = 6$$ 6. **Find $y$ using $y = -x$:** $$y = -6$$ **Final answer:** $$x = 6, \quad y = -6$$