Can you please explain these questions how to solve

Thanks in advance

I would appreciate it if you can explain the concept and the equation too.

1:: A diagram of a double slit experiment is shown. A location in the interference pattern is marked "a." For location a, the path length difference is 3. III b. it d. 43 b d e. 61 2:: How would you calculate the path length difference from the picture given? (In the following, each two-letter combo means the distance between those two points. E.g., bc is the distance between point b and point c.] C a. {ch b. {ch d. {ch lbc} e. {bd} [bc] 3:: A diagram of thin lm interference is shown with the various light rays labeled with roman A numerals Hi. The thin lm interference effect is lncrdem I ight observed when constructive or destructive \\ I I I interference occurs between waves I V a. I and III Air b. IandV \"1:130; c. II and IV d. "and Ill Water I I e. Illandv (n: 133} r 4:: The lowest wavelength for which destructive interference will occur to the eye can be found _ Glass plate \"5'"3 (n=1.52} a. A = b 21 = _ _ 2 phase flips, so no correction needed c 0.51 = 2|: d. A = 2r Destructive: 0.5L 1.5)., etc