Answer
$V_{rms} = 159~V$
Work Step by Step
In part (a), we found that $_{rms} = 2.586~A$
We can find the $rms$ voltage across $C$:
$V_{rms} = I_{rms}~X_C$
$V_{rms} = \frac{I_{rms}}{2\pi~f_d~C}$
$V_{rms} = \frac{2.586~A}{(2\pi)(550~Hz)(4.70\times 10^{-6}~F)}$
$V_{rms} = 159~V$
