Kirchoff's voltage law states that the sum of all voltages from power sources is equal to the total voltage.
Kirchoff's current law states that the current entering a node is the same as the current leaving.
And I'm sure you know ohms law.
So by analyzing the circuit you can find the current at certain nodes from each power source. Implicate through KCL what the current is it a common point. Then through Ohms law find the voltage.