To simplify the expression 7a + 2b + 5a + b, we start by combining like terms.
1. First, identify the terms that contain the variable a: 7a and 5a.
2. Add these two terms together: 7a + 5a = 12a.
3. Next, identify the terms that contain the variable b: 2b and b.
4. Remember that b can be written as 1b. Now add these two terms together: 2b + 1b = 3b.
5. Now, combine both results: 12a + 3b.
Therefore, the simplified expression is 12a + 3b.