The half-life of Radium-226 is 1590 years. If a sample contains 200 mg, how many mg will remain after 3000 years?

Hint: Recall $P = P_{0}e^{kt}$ where $P_{0}$ is the initial amount of such a substance, $P$ is the amount at a given time $t$ and$k$ is the exponential rate of decay. What would it mean if $P = .5 P_{0}$?