-2a²b + a² + 3ab² - b² + 2(a²b + 2ab)
Simplify the parenthesis first.
-2a²b + a² + 3ab² - b² + 2a²b + 4ab
Now, add like terms.
(-2a²b + 2a²b) + 3ab² + 4ab + a² + b²
Simplify.
3ab² + 4ab + a² + b²
That is the simplest it can be simplified.
~Hope I helped!~