To check your answer, use the box method or foil, whichever you prefer. When you use it, leave out the x in front of the parenthesis. The answer will come to x(28x^2+27x+5), then distribute the x. You will get your original answer.
We know that Y⊥B, and Z⊥B, which means both Y and Z are perpendicular to B, meaning that they both create 90° angles with B, and from that, we can make the conclusion that Y || Z
