Question 70832
Your answer is the same as answer b. And it is correct.
.
I suspect that the confusion came because you didn't recognize that they were identical
because the two terms in parentheses appear in reverse order. That doesn't make a bit of 
difference in multiplication. No matter what order they are in, if the three terms are there,
the product will be the same. [You could have had the 3z as the last multiplier and it
wouldn't have made your answer different from answer b.]
.
That was a good job of factoring, by the way.