This question is beyond me, and I have very little direction for solving it. I understand that the component of $\ B $ perpendicular to the x$x$-axis is 0, and that the component parallel along the x$x$-axis is doubled, which is where I assume the 2 on the denominator comes from.
I can't find anything in my lecture notes/online describing a general formula for the Biot-Savart Law for any point on the x-axis. Anyone have any ideas?
Here is diagram 4)b) mentioned in the question: