\(MCD:R1nt\left(R2//R3\right)\)
\(\Rightarrow R=R1+\dfrac{R2\cdot R3}{R2+R3}=5+\dfrac{15\cdot10}{15+10}=11\Omega\)
\(\Rightarrow I=\dfrac{\xi}{R+r}=\dfrac{12}{11+1}=1A\)
\(I=I1=I23=1A\)
\(U=IR=1\cdot11=11A\)
\(\Rightarrow U1=I1\cdot R1=1\cdot5=5V\)
\(\Rightarrow U23=U2=U3=U-U1=11-5=6V\)
\(\Rightarrow\left\{{}\begin{matrix}I2=U2:R2=6:15=0,4A\\I3=U3:R3=6:10=0,6A\end{matrix}\right.\)