How to calculate equivalent resistance in mixed circuit?
Things to note: -


Point A (open circuited) can be regarded as a voltage source in series with a single resistor.
Point B (open circuited) can be regarded as a voltage source in series with a single resistor.


So, if you work out the equivalent open circuit voltage at point A you get 24 volts. For point B, the equivalent open circuit voltage is 12 volts. All just simple potential divider rules.

The single resistor for each open circuit source is the parallel value of 6 ohms and 3 ohms (= 2 ohms). This can be calculated by using Thevenin's Theorem.

Then you have 12 volts feeding through a 2 ohm resistor in series with R5 in series with another 2 ohm resistor being fed by 24 volts.

The voltage difference (that drives current through the three rationalized resistors) is simply 12 volts i.e. 24 volts minus 12 volts. So 12 volts across 2 ohm + 3 ohm + 2 ohm produces a current of 1.7143 amps. That current flows from point A to point B in your circuit.

Now you have all the information you need to calculate the actual voltages at points A and B (hopefully) so can you take it from here?