1. **State the problem:** Simplify or evaluate the expression $4c - 2a$ given no specific values for $a$ and $c$. 2. **Understand the expression:** The expression $4c - 2a$ is a linear combination of variables $a$ and $c$ with coefficients 4 and -2 respectively. 3. **No further simplification:** Since $a$ and $c$ are different variables and no values or relations are given, the expression cannot be simplified further. 4. **Note on the second expression:** The second expression $2b^4 + 5$ is separate and not connected to the first. Since the user asked about the first expression, we focus on $4c - 2a$ only. **Final answer:** The expression remains $4c - 2a$ as it cannot be simplified further without additional information.