Just to confuse things... You *can* look at just the voltage source, 12 ohm, 4 ohm and 40 ohm resistor, create the Thevenin equivalent, and then add the 10 ohms.
Thevenin voltage = 240 * 40/(12 + 4 + 40) = 171.429 volts
Thevenin resistance = (12 + 4)||40 = (16 * 40)/(16 + 40) = 11.429 ohms.
So now you have a thevenin equivalent network of a 171.429 volt source in series with an 11.429 ohm resistor.
Now add your 10 ohms resistor:
Voltage across the 10 ohm = 171.429 * 10/(11.429 + 10) = 79.999 volts. 80 volts.
[and I'm sure you could do it with the Norton equivalent also, but I never was any good with that concept.]