Edwin hubble calculated the expansion rate of the universe. on what evidence did he base his calculation?
\l "\l " a. levels of background radiation
\l "\l " b. differences in redshift for galaxies
\l "\l " c. the existence of planets outside of our solar system
\l "\l " d. levels of helium in the universe

Edwin Hubble calculated the expansion rate of the universe. The evidence that he base his calculation is the differences in redshift for galaxies. The answer is letter B. the red shift of galaxies was directly proportional to the distance of the galaxy from earth.  It means that bodies farther away from Earth were moving away faster. The Hubble’s constant is the ratio of distance to redshift equal to 170 kilometers per second per light year of distance.