The Function $\mathrm{A}=\mathrm{A}_{0} \mathrm{e}^{-0.00693 \mathrm{x}}$ Models the Amount in Pounds of a Particular Radioactive Material

Multiple Choice

The function $\mathrm{A}=\mathrm{A}_{0} \mathrm{e}^{-0.00693 \mathrm{x}}$ models the amount in pounds of a particular radioactive material stored in a concrete vault, where $\mathrm{x}$ is the number of years since the material was put into the vault. If 500 pounds of the material are placed in the vault, how much time will need to pass for only 268 pounds to remain?

A) $95 \mathrm{yr}$
B) $90 \mathrm{yr}$
C) $100 \mathrm{yr}$
D) $180 \mathrm{yr}$