Write as a Single Logarithm natural log of z-3 natural log of x

$\ln (z) - 3 \ln (x)$

Simplify $- 3 \ln (x)$ by moving $3$ inside the logarithm.

$\ln (z) - \ln (x^{3})$

Use the quotient property of logarithms, $\log_{b} (x) - \log_{b} (y) = \log_{b} (\frac{x}{y})$ .

$\ln (\frac{z}{x^{3}})$