To solve the expression:

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

Since both terms have the same denominator, $x + 5$, we can combine the fractions by adding the numerators directly:

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

So, the simplified form of the expression is:

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

Would you like a detailed explanation, or do you have any questions?

Here are five related questions for further exploration:

1. What would happen if the denominators were different? How would you approach it?
2. How can you simplify complex fractions with different variables?
3. What if the expression had a subtraction sign instead of addition?
4. How do you determine restrictions on $x$ for fractions to avoid division by zero?
5. How do you handle cases where the numerator and denominator have common factors?

Tip: When adding or subtracting fractions, always check if you can combine them by using a common denominator.