2b(4a+a^2)

To help you understand what needs to be done, let's take a simple example:

5(10+4) when solved gives 5(14) = 70 OK?

So, using your problem above, you cannot add the terms within the brakets. There is another solution; multiply each term by the number outside the brackets;

5(10) + 5(4)

Keep the sign, you'll eventually get 70, like previously.

So, with that example, can you simplify your problem?