First sketch a Free-Body Diagram. (See attachment below. I am taking the car to be moving in the +x direction.)

Apply Newton's 2nd Law in each coordinate direction. Since we know that the car is decelerating, there is an acceleration in the x direction.

$\displaystyle \sum F_x = -f = ma$

$\displaystyle \sum F_y = N - w = 0$

You can get the normal force from the y equation, and then the acceleration from the x equation.

Then this is just a motion under constant acceleration problem. You know the initial speed and the acceleration, and you want the time at which the speed is 0 m/s. (Remember to do the unit conversion on the initial speed!)

That should give you a good start. If you have any more questions on this, feel free to ask.

-Dan