For the circuit of Fig. 30.17 , let $C=15.0 \mathrm{nF}, L=22 \mathrm{mH}$, and $R=75.0 \Omega .$ (a) Calculate the oscillation frequency of the circuit once the capacitor has been charged and the switch has been connceted to point $a$. (b) How long will it take for the amplitude of the oscillation to decay to $10.0 \%$ of its original value? (c) What value of $R$ would result in a critically damped circuit?