Maximum power transfer problem. Find the resistance
This is super simple; It's 12kOhm.
Why?
The 18kOhm resistor is in parallel with a voltage source, ie. it has NO influence on anything, throw it away..
The 6kOhm resistor is in series with a current source ie. it has NO influence on anything, throw it away..
What are you left with?
And so what is the output impedance of your circuit???
To get maximum power transfer you just need the load to have the same value as the output impedance of the circuit.
This should be easy enough for you to solve now. (He did solve it)