Answer
The missing length is 13.5 units
Work Step by Step
$\frac{18}{z}$=$\frac{40}{30}$ set cross products equal
40z=18$\times$30
40z=540
$\frac{40z}{40}$=$\frac{540}{40}$ Divide both sides by 40
z=13.5
The missing length is 13.5 units