To integrate the expression $2x + x$, we first simplify it:

$2x + x = 3x$

Now, the integral of $3x$ with respect to $x$ is:

$\int 3x \, dx = \frac{3x^2}{2} + C$

where $C$ is the constant of integration.

So, the result is:

$\frac{3x^2}{2} + C$

Would you like a more detailed explanation of the steps, or do you have any further questions?

Here are some related questions for further exploration:

1. What is the integral of $x^2$?
2. How would you integrate $4x^3$?
3. What is the meaning of the constant of integration in indefinite integrals?
4. How do you integrate a sum of terms like $3x + 2x^2 + 5$?
5. Can you explain the power rule for integration?

Tip: When integrating polynomials, the power rule states that $\int x^n \, dx = \frac{x^{n+1}}{n+1} + C$, where $n \neq -1$.