Find the power in the 2W resistor R6 using Thevenin's theorem.

Remove R6 from the circuit

Redraw the circuit after finding the resistance, RA of the parallel branch R3||R4.

Redraw the circuit and calculate the voltage across the break AB which is the voltage across RA = VT. Remember that 20V is dropped across R1 and also across R2+RA. Since R2 = RA = 5W half of the voltage is dropped across each resistor VT = 10V

Remove V1 and replace it with a short circuit

This action also short circuits R1 out of the circuit

Determine Resistance looking into the break AB = RT

RT = (RAxR2) / (RA+R2) + R5 + R7 = 14.5W

Determine the value of the current from the Thevenin equivalent circuit

I = VT/(RT + R6) = 10/16.5 = 0.606A

Power dissipated by R6 = I x I x R = 0.73 Watts