$$\frac{x^{3}z^{6}}{x^{4}z^{6}}$$
To divide powers of the same base, subtract the denominator's exponent from the numerator's exponent.$$x^{3-4}z^{6-6}$$
Subtract $4$ from $3$.$$\frac{1}{x}z^{6-6}$$
Subtract $6$ from $6$.$$\frac{1}{x}z^{0}$$
For any number $a$ except $0$, $a^{0}=1$.$$\frac{1}{x}$$