\([(R_1ntR_2)//R_3]ntR_4\\R=\dfrac{(R_1+R_2)R_3}{R_1+R_2+R_3}+R_4=5,5(\Omega)\\\Rightarrow I=\dfrac{\mathcal{E}}{R+r}=0,2(A)=I_4=I_{123}\\\Rightarrow U_4=0,8(V)\\U_{123}=I_{123}.R_{123}=0,3(V)=U_{3}\\\Rightarrow I_3=\dfrac{U_3}{R_3}=0,15(A)\\\Rightarrow I_1=I_2=I_{12}=I-I_3=0,05(A)\\\Rightarrow U_2=0,2(A)\\\Rightarrow U_{AB}=U_{AN}+U_{NB}=U_2+U_4=1(A)\)