=>R1//{R2 nt {R3//R4)}
\(\Rightarrow Ia=2=I1+I3\Rightarrow\dfrac{Um}{15}+I3\)
\(R3=R4\Rightarrow I3=I4\Rightarrow2I3=I2\Rightarrow I3=\dfrac{I2}{2}=\dfrac{\dfrac{Um}{R2+\dfrac{R3R4}{R3+R4}}}{2}=\dfrac{\dfrac{Um}{30}}{2}=\dfrac{Um}{60}\left(A\right)\)
\(\Rightarrow2=\dfrac{Um}{15}+\dfrac{Um}{60}\Rightarrow Um=24V\)
\(\Rightarrow I1=I234=\dfrac{24}{R1}=1,6A\)
\(\Rightarrow I3=2-1,6=0,4A=I4\)
\(\Rightarrow I2=2I3=0,8A\)