Wave Optics

Two beams of light having intensities I and 4I interfere to produce a fringe pattern on a screen. The phase difference between the beams is \(\pi / 2\) at point \(\mathrm{A}\) and \(\pi\) at point \(\mathrm{B}\). Then the difference between the resultant intensities at \(\mathrm{A}\) and \(\mathrm{B}\) is