A superhero is rendered powerless when exposed to 55 or more grams of a certain element. A 600 year old rock that originally contained 900 grams of this element was recently stolen from a rock museum by the? superhero's nemesis. The? half-life of the element is known to be 150 years.
?a) How many grams of the element are still contained in the stolen? rock?
?b) For how many years can this rock be used by the? superhero's nemesis to render the superhero? powerless?