1. Problem: Find how much $a + 2b$ is greater than $b - a$. 2. Formula: To find how much one expression is greater than another, subtract the smaller from the larger: $$\text{Difference} = (a + 2b) - (b - a)$$ 3. Work: $$= a + 2b - b + a$$ $$= a + a + 2b - b$$ $$= 2a + b$$ 4. Explanation: We combined like terms by adding $a$ and $a$ to get $2a$, and $2b - b$ to get $b$. 5. Final answer: $$2a + b$$