When simplifying you add exponents that appear in the numerator and subtract those that appear in the denominator.
[tex]\dfrac{z^{2}y^{3}}{y^{-3}z^{6}}=y^{3-(-3)}z^{2-6}=y^{6}z^{-4}[/tex]
Now negative exponents can be put in the denominator as positive exponents.
[tex]=\dfrac{y^{6}}{z^{4}}[/tex]
This corresponds to selection
a. y⁶/z⁴.
