I have been stuck at the following question for some time now. All help is appreciated.
The Attempt at a Solution
I have resolved the right side of the circuit into a 10 ohm resistor. I have also found the current in the 20 ohm resistor (0.4A). I then used Ohm's Law to get the current in the 10 ohm resolved resistor and found it to be 5A. Then using Kirchoff's Current Law, I got 5.4A in the unknown resistor R, which gives a resistance of 9.26 ohms.
This 9.26 ohms however disagrees with the given answer of 10 ohms.
Where have I went wrong? All help is appreciated!