The Decay of 243 Mg of an Isotope Is Given $$\mathrm { A } ( \mathrm { t } ) = 243 \mathrm { e } ^ { - 0.014 \mathrm { t } }$$

Multiple Choice

The decay of 243 mg of an isotope is given by $$\mathrm { A } ( \mathrm { t } ) = 243 \mathrm { e } ^ { - 0.014 \mathrm { t } }$$ where t is time in years since the initial amount of 243 mg was present. Find the amount (to the nearest milligram) left after 72 years.

A) 240
B) 89
C) 45
D) 87