If b=9, then the i's will cancel out in the middle. When you multiply the two i's together, it makes 27i^2, and i sqaured is negative one so it would be negative 27. -18i and 18i would cancel, and you'll multiply 2 and 6 to get 12.
-27+12=-15
sorry, I edited it and meant b. Sorry about that! b=9
