The function

$x(t)=-2\mathrm{.}71e^{-1\mathrm{.}45t}$

describes the position, in meters, of a particle on the $x$ axis as a function of time $t$ in seconds.

Find the particle's velocity $v(t)$ at time $t=3\mathrm{.}23s.$

$v(t)=$

$\frac{m}{?}$