Regarding the step (a) listed in the Hint 3, notice that for two point sources, there is an interference maximum if the optical path difference of a given point from the two sources is a multiple of the wavelength. Regarding the step (d) listed in the Hint 3, notice that if you draw a line parallel to the lines mentioned in the Hint 4 so that it intersects the corresponding conic section, the intersection points will be positioned symmetrically relative to the axis of the conic section.
Please submit the solution to this problem via e-mail to physcs.cup@gmail.com. There will be no more hints, but the Problem 5 will remain open for submissions until t 23:59 GMT, 21st May 2023.