In the given circuit, viewed from AB, the circuit can be reduced to an equivalent circuit as:
1
1 volt source in series with 10 Ω resistor
2
7 volts source in series with 2.4 Ω resistor
3
5 volts source in series with 10 Ω resistor
4
15 volts source in series with 2.4 Ω resistor