1. The problem is to simplify or understand the expression $3a + 4b$. 2. This is a linear algebraic expression involving two variables $a$ and $b$. 3. The expression consists of two terms: $3a$ means 3 times $a$, and $4b$ means 4 times $b$. 4. Since $a$ and $b$ are different variables, the terms cannot be combined further. 5. Therefore, the expression $3a + 4b$ is already in its simplest form. 6. If values for $a$ and $b$ are given, you can substitute and calculate the numerical result. Final answer: $3a + 4b$