The expression provided is:

$\frac{3x}{x + 5} + \frac{4x}{x + 5}$

Since both terms have a common denominator of $x + 5$, we can combine them by adding the numerators:

$\frac{3x + 4x}{x + 5} = \frac{7x}{x + 5}$

So, the simplified expression is:

$\frac{7x}{x + 5}$

Would you like a further breakdown or have any questions?

Here are 5 related questions to expand on this:

1. How would you simplify an expression with different denominators?
2. What happens if you factor the numerator and denominator further?
3. How does the solution change if one term had a different denominator?
4. How do you simplify expressions when variables are in both numerator and denominator?
5. What are some common methods for simplifying fractions?

Tip: When adding fractions with the same denominator, combine the numerators and keep the denominator as it is.