A conductor in the shape of a rectangular loop has length, a$=8$ mm and width, b$=6$ mm$.$ The conductor carries a current, I$=4$ x $104$ A$.$ Calculate the magnitude of the net magnetic field at the center of the rectangle $($By definition, center of rectangle is the point of intersection of the diagonals$).(0=4$ x$10-7$ T m$/$A$)$