In order to solve this problem you need to use phasor algebra. Phasor algebra has the advantage that it reduces steady-state sinusoidal circuits to the form of pure resistance circuits. Once the problem has been converted to the frequency domain it is essentially a resistive problem. The only difference is that the real-number algebra used for resistive circuits becomes complex-number algebra for frequency-domain circuits. I will presume you are proficient in doing simple arithmetic (add, subtract, multiply, divide) with complex numbers.

The circuit is a simple voltage divider in the frequency domain; therefore, structure the solution as a resistor voltage divider but then use impedance instead of resistance. For cutoff frequency I would assume that means the half-power point. Since power is proportional to the square of the voltage, (Vout/Vin)^2=1/2, what is the frequency where Vo/Vi=0.707?