Bubba wanted to know approximately how much copper is present in pennies minted after the year 1982.  First, Bubba chose his penny and filed a small notch on either side of the coin.  He then proceeded to weigh the penny.  Bubba, with the help of his science teacher, measured out 20 ml, or 6 cm, of hydrochloric acid into a 50-mL beaker.  Bubba then poured the acid into the beaker, covering the penny.  He left the cup sitting over night, and removed the penny with a pair of tongs on the next day.  Bubba then washed the pennies in water to remove all of the acid and dried them thoroughly.  He then weighed the penny again to determine the amount of copper left.