And we have the current which is flowing out of the inverting input,

which we know is zero, our first property of the ideal op-amp.

I'm going to add it in there for completeness.

And there's our sum.

So this is Kirchhoff's current law at node one.

So we can see from this that we have an equation which has one unknown,

V out, and we can solve for it.

If we solve for V out, we end up with V out equal to minus 15 volts.

Now we want to find I out.

And I out is our current back into the op-amp.

So we can use the node at the output, maybe we call this node two,

and we can use Kirchhoff's current law at node two to find that current I out.

So this is KCL at node two.

And again, we're going to sum the currents into that node.

We could choose to sum them out of the nodes, but for consistency,

we're going to sum the currents into the nodes.