light of wavelength 575 nm passes through a double slit and the third order bright fringe is seen at an angle of 6.5 away from the central fringe. what is the separation between the double slits

Awoman holds a book by placing it between her hands such that she presses at right angles to the front and back covers. the book has a mass of m = 1.8 kg and the coefficient of static friction between her hand and the book is μs = 0.67. no attempt 50% part (a) what is the weight of the book, fgb in newtons?