Wave Optics Part 1

In a double slit experiment with monochromatic light, fringes are obtained on a screen placed at some distance from the plane of slits. If the screen is moved by 5×10−2m towards the slits, the change in fringe width is 3×10−3‌cm. If the distance between the slits is 1‌mm, then the wavelength of the light will be____ nm.