Questions..........Can anyone help me out?

The impedance across a-b in the circuit is adjustable for maximum power transfer to Zab.


According to the circuit,


If I replaced the impedance across a-b by a variable resistor, what is the value of the variable resistor value that will yield maximum average power transfer to RL. What will be the value of maximum average power transferred to RL?

If the impedance across a-b is replaced by a variable impedance. What is the value of the variable impedance value that will yield maximum average power transfer to ZL? Then how should I get the maximum average power transferred to ZL


Can I use the Thevenin equivalent circuit with respect to the terminal a,b for the circuit? If can, how? Can anyone help me out? I want to confirm whether I am right or wrong for working into this question.