The image is missing, but I found it here:
https://session.masteringphysics.com/problemAsset/1000287485/3/wires.jpg
Solution:
We can use the right-hand rule to understand the direction of the magnetic field of each wire.
Let's start with the wire on the right. Let's put the thumb of the right hand as the direction of the current in the wire (out of the page), and let's "wrap" the other fingers around it. We can see that at point b, the other fingers are directed toward south, so this is the direction of the field generated by the right wire at point b.
Now let's repeat the procedure with the wire on the left. We can see that this time, the magnetic field at point b is directed toward north. Since the two wires carry equal currents, and point b is equally distant from both wires, we can conclude that the intensity of the two magnetic fields is equal, and since they are in opposite direction, the net field is just the difference of the two fields, so it will be zero.
