1. The problem statement, all variables and given/known data 2. Relevant equations B = μ0*i/(2PI*r) 3. The attempt at a solution First of all, if you're looking at this, that means you intend to help me study for my upcoming physics exam on a Friday night. If you fit into this category of people, then god bless your soul. I should state that I have all the answers to these, because the solutions are posted - I just want to ensure that I understand the material. Some of the solutions are illegible, but that's not a huge deal. So, I understand part a: I use the relevant equation that I typed and replaced 'i' with "i1" and "i2" and replaced 'r' with 'd.' After accounting for unit vectors, the correct answer is: B(vector) = μ0*(i1*x(vector) + i2*y(vector))/(2PI*d) So, let's start w/ part b: I have no clue what's going on besides that we need to find the force per unit length, which is F3 / L where L is length. The formula sheet equates F3 / L = i3 * B(total). Why is this the case?