From the above diagram, if each of the resistors can dissipate a maximum of 18W, the from the relation power, P = I²R, the current in the 2Ω series resistor is given by:
I² = P/R = ¹⁸/₂ = 9 => I = √9 = 3A
The effective parallel arrangement of the two 2Ω resistors: ¹/_R = ¹/₂ + ¹/₂ = 1Ω
∴ Total resistance in the circuit = 1 + 2 = 3Ω
current flowing the circuit = 3A
∴ Maxi. power = P = I²R = 3² x 3 = 27W