In rc low or high pass filter how to calculate cut-off frequency when a r is connected in parallel to c in low pass filter
What is the purpose of the DC source?
Regarding your question: You have nothing to do than to apply the DEFINITION of the cut-off frequency wc:

1.) Set the magnitude of the transfer function equal to Ao/SQRT(2) with Ao being the transfer function value for w=0. The value of Ao can be derived from the circuit by visual inspection neglecting the capacitor (1/wC approacing infinite).

2.) Alternative: Equalize the real and imag. parts of the complex tranfer function .