A plane monochromatic light wave with wavelength falls on the surface of a glass wedge whose faces

Question:

A plane monochromatic light wave with wavelength λ falls on the surface of a glass wedge whose faces form an angle a << 1. The plane of incidence is perpendicular to the edge the angle of incidence is θ1. Find the distance between the neighbouring fringe maxima on the screen placed at right angles to reflected light.