1. **State the problem:** Simplify the expression $x + x$. 2. **Recall the rule:** When adding like terms, you add their coefficients. 3. **Apply the rule:** $x$ can be written as $1x$, so $x + x = 1x + 1x$. 4. **Add the coefficients:** $1 + 1 = 2$, so $1x + 1x = 2x$. 5. **Final answer:** The simplified form of $x + x$ is $2x$.