1. **Problem:** Write the expression for "the number x doubled". 2. **Formula:** Doubling a number means multiplying it by 2. 3. **Expression:** If the number is $x$, then doubled is $2x$. 4. **Simplification:** The expression $2x$ is already simplified. 5. **Explanation:** Doubling means taking the number twice, so multiplying by 2 gives the doubled value. **Final answer:** $2x$