Can someone please help me solve this circuit board problem? According to the answer sheet the answer for Vab=18V and Vbc=3V, but I have no idea how they got there. Thanks.
You should do your homeworks by yourself.
However, as an hint, consider just one generator at a time (while the other is shorted) and calculate the voltage between the two nodes you want then apply the superposition. This means you will have Vab(1) with the 14V working and the 30V shorted and Vab(2) with the 30V working and the 14V shorted so Vab=Vab(1)+Vab(2). The same to calculate Vbc.
I would simply calculate the current in the loop, 1A (30V-14V and 16 ohms of resistance). The circuit is not complicated enough to need anything more. From the current, the voltage drops can be calculated.