1. **Problem:** Calculate the sum $2x + 8x$. 2. **Formula:** When adding like terms, add their coefficients and keep the variable the same. 3. **Work:** $$2x + 8x = (2 + 8)x = 10x$$ 4. **Explanation:** Since both terms have the variable $x$, we add the coefficients $2$ and $8$ to get $10$, so the result is $10x$. Final answer: $10x$