Amolecule that can be used as a molecular clock has a neutral mutation rate of one mutation per 20 million years. how many years ago did two species share a common ancestor if the molecules found in these two species differ by a total of six mutations?

The current thought on the structure of the cell membrane is: a. a static phosphate sandwich of lipids b. a fluid-mosaic of phospholipids and proteins c. a bilayer of proteins with static lipid molecules d. an impermeable bilayer of protein molecules e. a static and permeable phospholipid single layer