In Youngs Double Slit Experiment with two identical slits when upper slit is covered with a transparent sheet of mica second order minima observed above the centre of the screen and second order Maxima below it which of the following cannot be possible value of phase difference caused by mica sheet :

1.$ \pi /3$

2. $7\pi /2$

3.$ 10\pi/3$

4. $11\pi/3$

I can't get that which maxima because it can be at $-3\lambda/2 $ or $3\lambda/2$

and even further how shall I decide the phase difference ?