\[\frac{3z}{z^{2} - 2z} - \frac{8 - z}{z^{2} - 2z} = \frac{3z - 8 + z}{z^{2} - 2z} =\]
\[= \frac{4z - 8}{z^{2} - 2z} = \frac{4(z - 2)}{z(z - 2)} = \frac{4}{z}.\]