1. **State the problem:** Solve for $y$ in the equation $2x + 4 = -y$. 2. **Rewrite the equation:** The goal is to isolate $y$ on one side. Starting with: $$2x + 4 = -y$$ 3. **Multiply both sides by $-1$ to get $y$ positive:** $$\cancel{-1} \times (2x + 4) = \cancel{-1} \times (-y)$$ which simplifies to: $$-2x - 4 = y$$ 4. **Rewrite the equation with $y$ on the left:** $$y = -2x - 4$$ 5. **Explanation:** We multiplied both sides by $-1$ to change the sign of each term, isolating $y$. This is a linear equation in slope-intercept form $y = mx + b$ where $m = -2$ and $b = -4$. **Final answer:** $$y = -2x - 4$$