Physics circuit analysis question
I'm going to suggest the same thing I suggest every time questions involving lots of resistors arise. Circuits are topological, meaning that as long as you don't change which nodes are connected, you can draw the circuit however you like.

These questions are specifically formatted to be in a topology which is difficult to follow if you haven't yet built up the confidence to do so. Don't be afraid to redraw them into something more friendly. I tend to suggest you make everything vertical with sources increasing the distance of any node from the bottom of the diagram (they are adding voltage), and resistors decreasing the distance (they drop voltage). Furthermore, you can then unjumble the resistors to try and se which are in series and which are in parallel.

Here is the same diagram as the question redrawn. Hopefully now you can see where you went wrong on part (a).







simulate this circuit &ndash; Schematic created using CircuitLab