b
In the given circuit \(6 \,\Omega\) and \(3 \,\Omega\) are in parallel, and hence its equivalent resistance is given by

\(\frac{1}{R_{p}}=\frac{1}{6}+\frac{1}{3} \quad \text { or } \quad R_{p}=2 \,\Omega\).

The equivalent circuit diagram is given in figure.

Total current in the circuit,

\(I=\frac{18}{2+4}=3\, \mathrm{A}\).

Power in the circuit \( = VI = 18 \times 3 = 54\,\,watt.\)