Question 24.12: Apply Kirchhoff’s loop on the circuit of Example 24.8 to fin......

Applying Kirchhoff’s loop rule to the loop abb′a′a of Fig. 24.13, and traversing the loop clockwise, we obtain the following expression:
Loop abb′a′a:    {\mathcal{E}}_{1}+I r_{1}+I r_{2}-{\mathcal{E}}_{2}=0

9 V + (0.02 Ω)I + (0.04 Ω)I − 12 V = 0
Then: I = 50A
Of course, we do not need Kirchhoff’s rules to solve this simple loop circuit.
We are just using it to practice applying the loop rule.