I don't know how to solve this at all, i just need some help on how to figure it out. Thanks!

Answer:
[tex]\sf \dfrac{3}{{z-3} }[/tex]
Explanation:
[tex]\Longrightarrow \sf \dfrac{1}{z} \div \dfrac{z-3}{3z}[/tex]
apply the theorem when [tex]\dfrac{a}{b} \div \dfrac{c}{d}[/tex] then [tex]\dfrac{a}{b} \times \dfrac{d}{c}[/tex]
[tex]\Longrightarrow \sf \dfrac{1}{z} \times \dfrac{3z}{z-3}[/tex]
Join the fractions
[tex]\Longrightarrow \sf \dfrac{3z}{z({z-3)} }[/tex]
Cancel out common factor z
[tex]\Longrightarrow \sf \dfrac{3}{{z-3} }[/tex]
The answer is : [tex]\boxed {\frac{3}{z-3}}[/tex]
Remember that dividing fractions is the same as multiplying the 1st fraction by the reciprocal of the other.
[tex]\mathsf {\frac{1}{z} \div \frac{z-3}{3z}}[/tex]
[tex]\mathsf {\frac{1}{z} \times \frac{3z}{z - 3}}[/tex]
[tex]\mathsf {\frac{3}{z-3}}[/tex]