Answer
$C = 2.66\times 10^{-8}~F$
Work Step by Step
In part (a), we found that the frequency is $~~4.60\times 10^3~Hz$
We can find the capacitance:
$X_C = \frac{1}{\omega_d~C}$
$X_C = \frac{1}{2\pi~f~C}$
$C = \frac{1}{2\pi~f~X_C}$
$C = \frac{1}{(2\pi)~(4.60\times 10^3~Hz)~(1300~\Omega)}$
$C = 2.66\times 10^{-8}~F$
