\(10.\left(R_1ntR_2\right)//R_3\\ R_1ntR_2\Rightarrow R_{12}=R_1+R_2=8\Omega\\ R_{12}//R_3\Rightarrow R_{123}=\dfrac{R_{12}.R_3}{R_{12}+R_3}=\dfrac{8.4}{8+4}=\dfrac{8}{3}\Omega\\ 8.R_1nt\left(R_2//R_3\right)\\ R_2//R_3\Rightarrow R_{23}=\dfrac{R_2.R_3}{R_2+R_3}=\dfrac{6.4}{6+4}=2,4\Omega\\ R_1ntR_{23}\Rightarrow R_{123}=R_1+R_{23}=2+2,4=4,4\Omega\)