Long division, hmmm I think perhaps we can do something else about this, instead, you should have \left(z^{2}-6z+13\right)\left(...\right) using sum and product of roots.
Step 2 look at what we have here
\mathbf{z^{4}}-4z^{3}-3z^{2}+50z-\mathbf{52}.
In this case, your head should immediately go...