${{R}_{1,2}}={{R}_{1}}+{{R}_{2}}=10\Omega ,\frac{1}{{{R}_{1,2,3}}}=\frac{1}{{{R}_{3}}}+\frac{1}{{{R}_{1,2}}}=\frac{1}{40}+\frac{1}{10}=\frac{5}{40}\Rightarrow {{R}_{1,2,3}}=8\Omega $ ${{R}_{eq}}={{R}_{1,2,3}}+{{R}_{4}}=8+3=11\Omega $ $I=\frac{\varepsilon }{{{R}_{eq}}+r}=\frac{24}{11+1}=2A\Rightarrow I={{I}_{4}}={{I}_{1,2,3}}=2A$ $\left. \begin{matrix} {{V}_{3}}={{V}_{1,2}}\Rightarrow {{R}_{3}}{{I}_{3}}={{R}_{1,2}}{{I}_ {1,2}}\Rightarrow 40{{I}_{3}}=10{{I}_{1,2}}  \\ {{I}_{1,2}}+{{I}_{3}}=2A  \\ \end{matrix} \right\}\Rightarrow {{I}_{3}}=0/4A$