To simplify the expression $4a + 2a + 3b$, follow these steps:

1. Combine like terms: The terms $4a$ and $2a$ are like terms (both involve the variable $a$), so you can add them together: $4a + 2a = 6a$

2. Write the simplified expression: Now the expression becomes: $6a + 3b$ This is the simplest form, as $6a$ and $3b$ are not like terms and cannot be combined further.

So, the simplified expression is $6a + 3b$.

Would you like to explore how to factor expressions like this? Or have other questions on algebra?

Here are some related questions:

1. How do you factor expressions like $6a + 3b$?
2. What is the difference between like and unlike terms in algebra?
3. How can you simplify expressions with more variables, like $3a + 4b - 2a + 5b$?
4. How do you solve for $a$ or $b$ if given an equation with these terms?
5. What are the basic rules for adding and subtracting algebraic terms?

Tip: When combining like terms, ensure the variables and their exponents match. Only then can you perform the addition or subtraction.