Given here, phase difference at point A and B are ϕA=2πand ϕB=3π.
Resultant intensity at point A,
IA=I+4I+2I4Icos(2π)
⇒IA=5I+4I(0)=5I
Resultant intensity at point B,
IB=I+4I+2I4Icos(60∘) =5I+4I×21=7I
Difference in intensities is IB−IA=7I−5I=2I.
Thus, value of x=2.