U=120 V
P=400 W
R₁=20 Ω
R₂=30 Ω
[tex]P=U*I \ \ \rightarrow \ \ I=\frac{P}{U}=\frac{400}{120}=3,(3) \ A\\ \\I=I_1=I_{23}[/tex]
[tex]I=\frac{U}{R} \ \ \rightarrow \ \ U=I*R\\ \\U_1=I_1*R_1=3,(3)*20=66,(6) \ V\\ \\U_{23}=U-U_1=120-66,(6)=53,(3) \ V\\ \\U_2=U_3=U_{23}[/tex]
[tex]I_2=\frac{U_2}{R_2}=\frac{53,(3)}{30}=1,(7) \ A\\ \\I_3=I-I_2=3,(3)-1,(7)=1,(5) \ A[/tex]