$9.$ Your car is broken, so you$$re pushing it$.$ If your car has a mass of $800$ kg$,$ how much momentum does it have when it$$s moving forward at $3$ m$/$s $(11$ km$/$h$)?$

$10.$ You begin pushing the car forward from rest $($see Problem $9).$ Neglecting friction, how long will it take you to push your car up to a speed of $3$ m$/$s on a level surface if you exert a constant force of $200$ N on it$?($Answer: $12...$but what are the units?$)$

$11.$ No one is driving your car $($see Problems $9,10,$ and $11)$ and it crashes into a parked car at $3$ m$/$s$.$ Your car comes to a stop in just $0\mathrm{.}1$ s$.$ What force did the parked car exert on it to stop it that quickly? $($Answer: $24,000$ N on your car$$show how this is obtained$).$

Just need help with an equation for $11.$