Answer
$-3.8 \mathrm{m}/\mathrm{s}^{2}$
Work Step by Step
The acceleration of a moving object is the derivative of its velocity,
that is, the second derivative of the position function.
$v=\displaystyle \frac{ds}{dt},\qquad a=\frac{dv}{dt}$
$\displaystyle \frac{ds}{dt}=-3.8t$
$\displaystyle \frac{dv}{dt}=-3.8 \mathrm{m}/\mathrm{s}^{2}$
