Find the potential difference between points b and a in the circuit below
I have already solved for the voltages of the two batteries (1 and 2) in the circuit (18 V and 7 V respectively)
2. Homework Equations
1) Potential difference across any closed loop is 0
2) Current in = current out
The Attempt at a Solution
I have read that Kirchhoff's current rule is how to approach these kinds of problems, but I am not sure how.