Population of a town at time t is given by the differential equation ${dP(t)\over dt}=(0.5)\ P(t)-450$. Also P(0) = 850 find the time when population of town becomes zero.
(1) $\ln9$
(2) $3\ln4$
(3) $2\ln18$
(4) $\ln18$
(1) $\ln9$
(2) $3\ln4$
(3) $2\ln18$
(4) $\ln18$