What is the Ratio of I1 to I2 for Zero Magnetic Field at Points A, B, and C?

[sphys4]

Homework Statement

Because of the 2 wires in the figure,
For what value of the ratio I1/I2 is the magnetic field zero at the point A? point B? point C?

Homework Equations

http://tinypic.com/r/5otweg/7

The Attempt at a Solution

I honestly have no idea where to start with this problem, any help is appreciated!

I tried to upload the picture and it seems to not be working for me? My computer is really old so i don't know if its just not loading, if not here's the figure. http://tinypic.com/r/5otweg/7

 

[ideasrule]

Assuming the bottom wire didn't exist, do you know how to calculate the magnetic field (both magnitude and direction) due to the first wire at A, B, and C? How about if the bottom wire was there, but the top one wasn't? The total magnetic field is just the vector sum of the contributions due to each wire.

 

[sphys4]

Assuming the bottom wire didn't exist, do you know how to calculate the magnetic field (both magnitude and direction) due to the first wire at A, B, and C? How about if the bottom wire was there, but the top one wasn't? The total magnetic field is just the vector sum of the contributions due to each wire.

Well then i would have to use B = ul/2pir?
So do i just find that for each of the wires and then add them together?