$\text{a)}$

$\text{R = R1 + R2 = 6 + 10 = 16}$$(\Omega)$

$\text{I = I1 = I2}$ $=\frac{U}{R}$ $=\frac{12}{16}=0,75 (A)$ $\text{(R1 nt R2)}$

$\text{b)}$

$\text{ Công suất tiêu thụ:}$

$\left \{ {{U1=I1.R1=0,75.6=4,5 (V)} \atop {U2=I2.R2=0,75.10=7,5 (V)}} \right.$ 

$\Rightarrow$ $\left \{ {{P1=U1.I1=4,5.0,75=3,375(W)} \atop {P2=U2.I2=7,5.0,75=5,625 (W)}} \right.$ 

$\text{c)}$

$\text{R' = R1 +}$$\frac{R2.R3}{R2 + R3}$

$\text{R' = 6 +}$ $\frac{10.15}{10+15}= 12$$(\Omega)$

$\Rightarrow$$\text{I' = I1' = I23}$$=\frac{U}{R'}$$=\frac{12}{12}=1A$$\text{(R1 nt R23)}$

$\text{U23 = U2 = U3 = I23 . R23}$

$\text{= 1}$$(\frac{10.15}{10 + 15})=6V(R2//R3)$

$\Rightarrow$ $\left \{ {{I2=U2÷R2=6÷10=0,6A} \atop {I3=U3÷R3=6÷15=0,4A}} \right.$