The relative abundance of ⁴⁰K (molecular mass 40.0 g/mol) is 1.2 × 10^-4. The isotope 40K is radioactive with a halflife of 1.3 × 10⁹ y. Potassium is an essential element of every living cell. In the human body the mass of potassium constitutes approximately 0.36% of the total mass. Determine the activity of this radioactive source in a student whose mass is 60 kg.