It is known that 7008 mg of radioactive material scattered into the environment as a result of accident disappears at a rate proportional to its amount. Since it is determined that after 4 years, 31% of the initial mass of the substance has disappeared;

a)Calculate the mass of the substance remaining in the environment after 12 years. b) Calculate the half-life of the substance. c) Calculate the decay constant when 80% of the matter is destroyed after 100 years.