Find I_x in the network.
We will find the power in terms of I_x and then solve for I_x at the end. Remember that power is current multiplied by the voltage.
We know that there are 2 sources which supply power (they are the red sources, and you can see that the current enters the negative terminal of those sources, which means power is supplied)
Therefore, we can say that the total power absorbed by the other elements must equal the total power supplied by the other 2 elements.
Isolating for I_x gives us: