The answer is
First multiply b and b, it will then give you
Then multiply b and -4, that will give you -4b.
Third multiply b and -2, that will give you -2b.
Since -4b and -2b are with the same variable you can add them which will give you -6b.
Then multiply -4 by -2, which will give you 8 as a result.
Then arrange and will finally give you the answer: