Let us simplify the given expression step by step:

Problem: Simplify $3(5 - 2n) + 9n$

1. Distribute $3$ across $(5 - 2n)$: $3 \cdot 5 - 3 \cdot 2n = 15 - 6n$

   Now the expression becomes: $15 - 6n + 9n$

2. Combine like terms ($-6n + 9n$): $15 + 3n$

The simplified expression is: $15 + 3n$

Answer: Option (4): $15 + 3n$

Would you like me to explain any steps further or provide related examples?

Related Questions:

1. How do you apply the distributive property to expressions?
2. What is the importance of combining like terms in algebra?
3. How do you verify simplified expressions?
4. What is the difference between simplification and solving equations?
5. How do you factorize expressions like $15 + 3n$?

Tip:

Always distribute carefully and watch the signs when simplifying expressions. Missteps with negative signs are common in algebra!