Write the Word or Phrase That Best Completes Each Statement $\mathrm { A } ( \mathrm { t } ) = 450 \mathrm { e } ^ { - .168 \mathrm { t } }$

Multiple Choice

Write the word or phrase that best completes each statement or answers the question.
-How long will it take a sample of radioactive substance to decay to half of its original amount, if it decays according to the function $\mathrm { A } ( \mathrm { t } ) = 450 \mathrm { e } ^ { - .168 \mathrm { t } }$ , where $\mathrm { t }$ is the time in years? Round your answer to the nearest hundredth year.

A) $4.13 \mathrm { yr }$
B) $36.36 \mathrm { yr }$
C) $75.60 \mathrm { yr }$
D) $40.49 \mathrm { yr }$