Hubble's Law

Hubble's Law was written on a small whiteboard in Miss Quill's physics classroom, expressed as: $$v = H_0\,d$$ The board also stated that: $$z = \frac {v}{c} = \frac {H_0\,d}{c}$$ And that rearranging this would give: $$\frac{r}{L_1} = \frac{\mbox{distance to a galaxy}}{t\mbox{'s speed of recession}}$$ (TV: Detained)