Finding voltage in RLC circuit
You have a fixed frequency (4kHz), series RLC circuit with a constant peak Vin of 2.6V, so you can think of it as a voltage divider.

Work out your reactances at 4kHz and Vout will be proportional to Vin.

$$ X_C = \frac{1}{2\pi fC}\Omega = \frac{1}{2\pi(4000)(10^{-6})}\Omega$$
$$ X_L = {2\pi fL}\Omega = {2\pi(4000)(2.2\times10^{-3})}\Omega$$
$$ V_{OUT} = V_{IN}\frac{(X_L+R)}{(X_L+X_C+R)} $$

Hope this helps!