The displacement current in a capacitor is the same as the conduction current. The capacitive reactance \(X_c\) is given by:
\[ X_c = \frac{1}{\omega C} = \frac{1}{2 \pi f C} \]
Substituting the given values:
\[ X_c = \frac{1}{2 \pi \times 4 \times 10^3 \, \text{Hz} \times 12 \times 10^{-6} \, \text{F}} \approx 3.317 \, \Omega \]
The current \(I\) is given by:
\[ I = \frac{V}{X_c} = \frac{40 \, \text{V}}{3.317 \, \Omega} \approx 12 \, \text{A} \]