$(07\mathrm{.}01MC)$

The concentration $of$ a medication $Minm\frac{g}{L}$ present $in$ the bloodstream decreases over time such that the concentration $of$ medication $is$ proportional $to$ the amount $of$

medication $t$ hours after the first dose. The concentration $of$ medication $30$ minutes after the first dose $is80m\frac{g}{L}$ and was decreasing $at$ a rate $of150m\frac{g}{L}$per hour.

Which differential equation represents this relationship?

$\frac{dM}{dt}=-1\mathrm{.}25M$

$\frac{dM}{dt}=-0\mathrm{.}063M$

$\frac{dM}{dt}=-0\mathrm{.}66M$

$\frac{dM}{dt}=-1\mathrm{.}875M$