从左到右节点电压分别为Un1,Un2,Un3
(Un1-Un2)/2+(Un1-Un3)/3=4
(Un1-Un2)/2=Un2/8+(4+Un2-Un3)/6
(Un1-Un3)/3+(4+Un2-Un3)/6=Un3/2
解得Un1=12V,Un2=8V,U3n=6V