Answer
$\Delta t=6.1s$
Work Step by Step
To find the time required to stop, use the kinematics equation $$a=\frac{\Delta v}{\Delta t}$$ Solve for $\Delta t$ to get $$\Delta t=\frac{\Delta v}{a}$$ Substitute known values of $a=-9.1m/s^2$ and $\Delta v=-55.6m/s$ to get a time of $$\Delta t =\frac{-55.6m/s^2}{-9.1m/s^2}=6.1s$$
