The Amount Of ${ }_{18}^{40} \mathrm{Ar}$ Is One-Ninth the Amount Of ${ }_{19}^{40} \mathrm{~K}$

Multiple Choice

The amount of ${ }_{18}^{40} \mathrm{Ar}$ is one-ninth the amount of ${ }_{19}^{40} \mathrm{~K}$ . If the half-life of the latter is $T$ , what is the rock's age?

A) $T$
B) $T / 9$
C) $9 T$
D) $\ln (9 T)$
E) $T / \ln 9$
F) Some other result (specify)