The Decay Of $200 \mathrm{mg}$ Of an Isotope Is Given By $\mathrm{A}(\mathrm{t})=200 \mathrm{e}^{-0.012 \mathrm{t}}$

Multiple Choice

The decay of $200 \mathrm{mg}$ of an isotope is given by $\mathrm{A}(\mathrm{t}) =200 \mathrm{e}^{-0.012 \mathrm{t}}$ , where $t$ is time in years since the initial amount of $200 \mathrm{mg}$ was present. Find the amount left (to the nearest $\mathrm{mg}$ ) after 71 years.

A) $84 \mathrm{mg}$
B) $43 \mathrm{mg}$
C) $198 \mathrm{mg}$
D) $85 \mathrm{mg}$