The situation can be represented by the following equation: \(z=\frac{k}{xy}\) where k is a constant of proportionality. Plugging in the given values: \(0.5=\frac{k}{2\times4}\) from which k = 4. When x = 4 and y = 9 \(z=\frac{4}{4\times9}=\frac{1}{9}\)
