1. The problem statement, all variables and given/known data http://s619.photobucket.com/albums/tt272/babyazureyoshi/?action=view¤t=014.jpg 2. Relevant equations 1) B_x = (µ_0 * I) / 2R at x = 0 3. The attempt at a solution I know that segments BC and DA do not contribute to the magnetic field at O so all I need to know is the contribution for segments AB and CD. Using equation one, I simplified the formula to ((µ_0 * I) / 2) * ((1/0.6) +(1/0.4)).