Answer
$f = 8840~Hz$
Work Step by Step
We can find the operating frequency:
$X_C = \frac{1}{\omega_d~C}$
$X_C = \frac{1}{2\pi~f~C}$
$f = \frac{1}{2\pi~C~X_C}$
$f = \frac{1}{(2\pi)~(1.50\times 10^{-6}~F)~(12.0~\Omega)}$
$f = 8840~Hz$