This question is basically asking you to apply the inverse square law. You know the initial value of the field, and you know the distance between rows. So, you can calculate how much less the magnetic field is when you move from the first row to the second row. Remember that B ~ 1/r^2

Distance between rows is 1.25cm Initial value of the field is 3.66G

Could someone show me how to calculate this problem? I asked my teacher and she sent me the above reply. Thank You