Element A in the diagram absorbs 30 W of power. Calculate V_x.
In our question, element A absorbs power which means current should be entering the positive terminal, however, we can see that in the diagram, current is in fact going in the opposite direction.
We know that p=vi
We need to find V_x so we will isolate for v.
Substituting our values gives us:
This question can be found in Basic Engineering Circuit Analysis, 10th edition, chapter 1, question 1.23.