Pls help

K A superhero is rendered powerless when exposed to 35 or more grams of a certain element. A 400 year old rock that originally contained 250 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? a) The stolen rock still contains about |grams of the element. (Do not round until the final answer. Then round to two decimal places as needed.)