When astronomers observe the spectra of distant galaxies, they notice that the hydrogen emission lines are shifted noticeably toward the red end of the visual spectrum, a phenomenon called red shift. red is lowest frequency of visible light. what does red shift indicate about the movement of the distant galaxies?

We interpret that to mean that the object is moving away from us. So far, that's the only way we know of that light can get red-shifted.

The other question you should think about is;. How do we know what the wavelength of that light WAS when it started out toward us ?

i would think it's food chain

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.