Worked example - how far is a galaxy receding at 7,000 km/s? Use Hubble's law v = H0 x d with H0 = 70 km/s/Mpc. Step 1: rearrange d = v / H0 = 7000 / 70 = 100 Mpc. Step 2: convert to light-years: 1 Mpc = 3.26 million light-years, so 100 Mpc = 326 million light-years. So its light has travelled 326 million years to reach us - we see it as it was when dinosaurs had not yet appeared (they arose ~230 million years ago). Note: this simple law works well for nearby galaxies; for very distant ones, relativistic cosmology is needed.