The information seems to pertain to optics, specifically the thin-lens equation and magnification. However, a clear question isn't presented. With provided fragments, the subject likely involves the physics of lenses and light interference patterns.
It appears that you're asking about lens equations and the magnification (m) in optics, which are typically covered in physics. However, the details provided are fragmentary and do not articulate a clear question. With the given fragments, it seems likely that you are working with the thin-lens equation 1/f = 1/di + 1/do, where f is the focal length of the lens, di is the image distance, and do is the object distance.
There's also a mention of magnification, which in optics is given by the equation m = -di/do, where a negative magnification implies that the image is inverted relative to the object. The figure and context you referenced are not provided, so it is difficult to give a precise answer.
If you are studying the interference pattern created by a laser and a movable mirror (as suggested by the mention of a red laser light and fringe crossings), this involves calculating the change in path length when the mirror is moved. This concept is related to the wave nature of light and is used to determine the wavelength of light based on the interference pattern observed.