Carel,

one good ay to start this work is by writing down the complex impedances of the components as a function of frequency. You should be able to do this, otherwise the assignmnet given to you would be useless. So:

X(L1) = f1(f)

X(R1)=f2(f)

X(C1)=f3(f)

where f1...f3 are the frequency dependend functions for the impedance of the components L1, R1 and C1 and f is the frequency.

Step 2 would be to write down the network equations.

2.1: Look at R1 and C1, this circuit can be replaced by a single complex impedance X(CR). To do this, forget L1 for a while, look only at R1 and C1 and the circuit they make.

2.2: Having replace R1 and C1 by a single impedance X(CR), now include L1 into the equation. What kind of circuit make X(CR) and X(L)? Calculate Vout as a function of Vin, X(L1) and X(CR).

Step 3: Now you should have something like Vout=Vin*foo(f) where foo(f) is the complex equation you have developed in the other steps. You next convert this to Vout/Vin=foo(f).

Step 4: From foo(f) you can find the amplitude and phase of the transfer function with respect to frequency. By putting the desired phase and/or amplitude into these equations and solving for the frequency f you'll arrive at the result.

This is the "hard" way, the way I was meant to learn it. Of course, you could built the circuit and find the result by testing and measuring it. Or you could use a simulator like SPICE. But both these ways will not help you gain insight about what's going on in the circuit.

Harald