Jai was measuring the radioactivity of different radioactive isotopes. Isotope A had a starting radioactive level of 50 g, and after 4 days it measured at 30 g. Isotope B had a starting radioactive level of 75 g, and after 4 days it measured at 25 g. Which best explains the isotopes?

Isotope A has a shorter half-life than Isotope B.
Isotope A has a longer half-life than Isotope B.
Isotope A has half the half-life of Isotope B.
Isotope A has twice the half-life of Isotope B.