Determine the voltage across the 5.0-Ω resistor in the drawing
You can use superposition. 

Replace each pair of voltage sources in turn, leaving one, with a short and calculate the voltage at the T-junction for each, then add all three voltages. 

So you'd be adding the voltage due to the 10V battery, the voltage due to the 2V battery and the voltage due to the 15V battery to get the total. 

The difference between that and the other side of the 5\$\Omega\$ resistor is your answer.