How to solve this circuit?
This is actually a very simple circuit, after making use of the following facts:


Elements in parallel to a voltage source can be omitted
Elements in series with a current source can be replaced by a short circuit


The voltage sources set the node voltage at node A to -5V, since two of them cancel each other.

At node B we have 5 currents, three are known. The other two can be written using the two node voltages VA and VB and the resulting equation can be solved. VA is already known, so only VB needs to be calculated.

The only resistors to care about are R4 and the two 50ohm resistors to the right. Everything else is unimportant.