What value of the load resistor R will extract the maximum amount of power from the circuit below, and how much power will that be?

4Ω 4Ω 6Ω a
│-----------/\/\/\-------------/\/\/\-------------/\/\/\/\---------◦----
​│ ​│ │ │
︴2Ω ↑ 3A ︴8Ω ︴R
│_____________│___________│____________◦__│
b