slit width = a , slit seperation = b = d (at photo),
Iq=Imx(cosB)^2 x (sinα/α)^2//
The Attempt at a Solution
My first move was to find intensity but I have no idea about the probability of finding one photon on the detector since It is not a point and It has own length.Should I think the detector as a point ? Location can be relevant with fringes but I'm not sure.