This top circuit has 2 voltage sources. The bottom circuit shows what the voltages and currents would be if just the one power supply were in the circuit. The other bottom circuit shows what the voltages and currents would be if just the other power supply were in the circuit. Look at the 1 K resistor there is 652 uA or 0.652 mA down on one circuit and 1.96 mA up on the other circuit. The Net result is 1.31 mA up on the top circuit. The voltage across that same resistor is 652 mV or 0.652 V. On one circuit. The voltage is -1.96 V on the other. The net result is -1.3 V on the top circuit.
