\(R_{23}=\dfrac{R_2\cdot R_3}{R_2+R_3}=\dfrac{10\cdot10}{10+10}=5\Omega\)
\(R_N=R_1+R_{23}=6+5=11\Omega\)
\(I_m=\dfrac{\xi}{r+R_N}=\dfrac{12}{1+11}=1A\)
\(U_1=I_1\cdot R_1=I\cdot R_1=1\cdot6=6V\)
\(U_2=U_3=U_{23}=I_{23}\cdot R_{23}=1\cdot5=5V\)
\(P_N=\xi\cdot I=12\cdot1=12W\)
\(A_N=P\cdot t=12\cdot10\cdot60=7200J\)