1. **State the problem:** Simplify the expression $-y4 - y4$. 2. **Understand the terms:** Here, $y4$ means $y \times 4$ or simply $4y$. 3. **Rewrite the expression:** $$-y4 - y4 = -4y - 4y$$ 4. **Combine like terms:** Both terms are like terms (both have $y$), so add their coefficients: $$-4y - 4y = (-4 - 4)y = -8y$$ 5. **Final answer:** $$-8y$$ This means the expression simplifies to $-8y$.