Problem C15:
In the figure above there are 4 wires that are perpendicular to the screen.
The current in the wires are +1 Amp, n_{1} Amp, n_{2} Amp, and +3 Amp.
**The "+" direction is out of the screen.** If the closed path
integral of **B**⋅**dl** = μ_{0} n_{3} where n_{3}
is the number of Amps, what is n_{3}.
Note that the direction of the path integral is **clockwise**.

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