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

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

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

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

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Well, how do I find power?

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

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Here we used Kirchoff's Law.

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

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

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

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

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I need to have voltage
difference in the current, or

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voltage difference in resistance,
or current in resistance.

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

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

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So how can I get voltage difference?

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

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

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

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Sure, voltage difference is
current times resistance.

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So I have current, and I have resistance.

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

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

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

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

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And then, kind of here in a line,

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

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So let's see how we do that.

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Let's flip this over.

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

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I also know my resistances.

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So the next thing I'm going to do.

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

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

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the voltage difference
is going to be V3 here.

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So V3 is going to be I3 times R3.

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

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

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

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

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

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So, the power is equal to VS2 times Is,

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which is equal to I3R3 times Is.