a. \(\left[{}\begin{matrix}R=\dfrac{U^2}{P}=\dfrac{220^2}{880}=55\left(\Omega\right)\\P=UI\Rightarrow I=\dfrac{P}{U}=\dfrac{880}{220}=4\left(A\right)\end{matrix}\right.\)
b. \(A=Pt=880.4.30=105600\left(Wh\right)=105,6\left(kWh\right)\)
\(\Rightarrow T=A.1800=105,6.1800=190080\left(dong\right)\)