1. **State the problem:** Simplify the expression $3x + 2x$. 2. **Recall the rule:** When adding like terms, add their coefficients and keep the variable the same. 3. **Apply the rule:** $$3x + 2x = (3 + 2)x$$ 4. **Simplify the coefficients:** $$3 + 2 = 5$$ 5. **Write the final simplified expression:** $$5x$$ So, the simplified form of $3x + 2x$ is $5x$.