A circuit consists of an AC source, for which \(\mathscr{E}_{\max }=\) \(18 \mathrm{~V}\), in series with a \(1200-\Omega\) resistor and a capacitor. If the amplitude of the potential difference across the resistor is \(V_{R}=9.0 \mathrm{~V}\) when the source operates at \(1500 \mathrm{~Hz}\), what is the capacitance of the capacitor?