a,\(I_1=I_2=\frac{U}{R_1+R_2}=\frac{36}{10+8}=2\left(A\right)\)
\(I_3=I_4=\frac{U}{R_3+R_4}=\frac{36}{12+24}=1\left(A\right)\)
b,để I qua các R bằng nhau thì
\(R_1+R_2=R_3+R_4\)
\(\Rightarrow R_4=\left(R_1+R_2\right)-R_3=18-12=6\left(\Omega\right)\)