A 105-milligram sample of a radioactive substance decays according to the equation

N=105 *e^-0.038t

whereNis the number of milligrams present aftertyears.

(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.