In a compact cicrcualr coil "A" (radius R= 25cm),formed by N=150 loops of wire, flows  I=10A current.
There's another compact circular coil "B" over "A"(radius r= 1.5 cm, loops n= 30)  coaxial with "A" distant X ,in which i= 4A flows .
in the same direction of "I" (look at the image).

Calculate  the mutual force between the two coils, and is it repulsive or attractive ?
Calculate X value when the force is Maximum.



HELP ME I  DON'T KNOW HOW TO SOLVE IT.....sorry for the translation English isn't my mother tongue.


IMAGE IN HIGHER RESOLUTION: http://img179.imageshack.us/img179/7660/bobinacn6.jpg