R1 nt (R2//R3) nt {R4 //(R5 ntR6)}
a,\(=>Rtd=R1+\dfrac{R2R3}{R2+R3}+\dfrac{R4\left(R5+R6\right)}{R4+R5+R6}=30\Omega\)
b,\(=>I1=I23=I456=\dfrac{Uab}{Rtd}=\dfrac{30}{30}=1A=>U23=U2=U3=I23.R23=\dfrac{R2.R3}{R2+R3}=2,4V=>I2=\dfrac{2,4}{R2}=0,6A=>I3=I23-I2=1-0,6=0,4A\)
\(=>U456=U4=U56=I456.R456=\dfrac{R4\left(R5+R6\right)}{R4+R5+R6}=15V=>I4=\dfrac{15}{R4}=0,5A=>I5=I6=1-0,5=0,5A\)
c,\(=>U6=I6R6=0,5.15=7,5V=>P6=U6I6=7,5.0,5=3,75W\)