$13\mathrm{.}41$ An engineer designing a system to control a router machining process models the system so that the router's acceleration $($in in $\frac{?}{s^2})$ during an interval of time is given by $a=-0\mathrm{.}4v,$ where $v$ is the velocity of the router in in$/$s$.$ When $t=0,$ the position is $s=0$ and the velocity is $v=2i\frac{n}{s}.$ What is the position at $t=3s?$