A 105-milligram sample of a radioactive substance decays according to the equation
N=105 * e^-0.038t
where N is the number of milligrams present after t years.
(a) Find the half-life of the substance to the nearest tenth of a year.
The half-life is _________ years.
(b): After how many years, to the nearest tenth of a year, there will be 105/4 milligrams present?
After _______ years there will be 26.25=105/4 milligrams of the substance left.