Thanks for setting up the Problem_Testing set.
Also the being careful about having random variables that could be zero. I think there are two issues - one about division by zero and the other about not ending up with the type of problem you intended.
I thought I had taken care of the division by zero problem by not letting $c, $d be zero. I think that I need to check Question 4 again - it was added later and I might have not chosen the denominator wisely.
About the type of question I wanted, reviewing the coefficients I need to make sure that $a is not zero so that I have a z-term in the parts that I want them in.
Thanks for looking at my question for me.