To solve this problem you must apply the proccedure shown below:
1. You have the following expression given in the problem above:
(3a²-5ab+b²)+(-3a²+2b²+8ab)
2. Therefore, you have:
3a²-5ab+b²-3a²+2b²+8ab
3ab+3b²
3. To simplify the expression you can factor 3b, as following:
3b(a+b)
Therefore, the answer is: 3b(a+b)