Answer
$\Delta t=2.8s$
Work Step by Step
To find the time needed for the change in velocity, use an equation relating change in velocity, change in time, and acceleration, which is $$a=\frac{\Delta v}{\Delta t}$$ Solve for $\Delta t$ to get $$\Delta t=\frac{\Delta v}{a}$$ Using determined values of $\Delta v=-11m/s$ and $a=-4.0m/s^2$ (see Answer 28a for explanation) to get a change in time of $$\Delta t=\frac{-11m/s}{-4.0m/s^2}=2.8s$$
