On the bottom because I can
see that you couldn't see it.

Okay, when we first started this
problem we were given Vs Is and that

the resistances and we were asked to find
all of the currents which we just did.

Now we'd like to be able to find
the power from this particular source.

Well, how do I find power?

Let me look in my toolbox of
possible equations to use.

Here we used Kirchoff's Law.

And here is how we, and
this is how we calculate power.

So when I had Kirchhoff's Law I
knew my current source and

my voltage source and my resistance and
I was able to calculate current.

Now, if I want power,
I need to have one of these three things.

I need to have voltage
difference in the current, or

voltage difference in resistance,
or current in resistance.

Here I have,
can I have voltage difference and current?

I certainly have current, I've got I but
I don't have voltage difference.

So how can I get voltage difference?

Well, there are several tools that I
have for getting voltage difference.

And this is actually the one
that I'm going to use.

If I have, oops, is that the one I want?

Sure, voltage difference is
current times resistance.

So I have current, and I have resistance.

Right here I have current and resistance,
so I can get voltage difference.

So watch how I'm going
to solve this problem.

I'm going to use Kirchoff's Law with
my known sources to find current.

And then I'm going to use my current and
resistance to find voltage difference.

And then, kind of here in a line,

I'm going to use my voltage difference and
my resistance to find power.

So let's see how we do that.

Let's flip this over.

Okay, now I know I one,
two, three, and IX.

I also know my resistances.

So the next thing I'm going to do.

Remember I use my
Kirchoff's Law to get those.

Now I'm going to use Ohm's Law to
find the voltage difference, and

the voltage difference
is going to be V3 here.

So V3 is going to be I3 times R3.

That's the same voltage difference
that is across this current source, so

if I had V current source, let's call
it VS2, that would be equal to V3.

Now, I've used my Kirchoff's Law
to find my current.

I've used my Ohm's Law to
find my voltage difference.

And now, I want to use my Power
equation in order to find the power.

So, the power is equal to VS2 times Is,

which is equal to I3R3 times Is.