A 0.10 mm wide slit is illuminated by light of wavelength 566 nm

A 0.10 mm wide slit is illuminated by light of wavelength 566 nm. Consider a point P on a viewing screen on which the diffraction pattern of the slit is viewed; the point is at 30° from the central axis of the slit. What is the phase difference between the Huygens wavelets arriving at point P from the top and midpoint of the slit? [Hint: Δϕ =(2π/λ)(Δx sin θ).]