${{V}_{2}}={{R}_{2}}{{I}_{2}}\Rightarrow {{V}_{2}}=2\times 4=8V$ ${{V}_{1}}+{{V}_{2}}=V\Rightarrow {{V}_{1}}+8=32V\Rightarrow {{V}_{1}}=24V$ ${{I}_{1}}=\frac{{{V}_{1}}}{{{R}_{1}}}=\frac{24}{4}=6A$ ${{I}_{3}}={{I}_{1}}-{{I}_{2}}=6-4=2A$ ${{V}_{3}}={{V}_{2}}=8V\Rightarrow {{R}_{3}}=\frac{{{V}_{3}}}{{{I}_{3}}}=\frac{8}{2}=4\Omega $