(d) Suppose current though different paths of the circuit is allows :
After applying $KVL$ for loop (1) and loop (2)
We get $28i_{1} = - 6 - 8 \Rightarrow i_{1} = - \frac{1}{2}A$
and $54i_{2} = - 6 - 12 \Rightarrow i_{2} = - \frac{1}{3}A$
hence$\ i_{3} = i_{1} + i_{2} = - \frac{5}{6}A$