What Is the Average Force Exerted by Car Brakes During a Stop?

[Knowneo]

The question is:
The driver of a car whose weight is 13000 Newtons traveling at 108km/hr slams on the brakes in order to undergo a constant acceleration, skidding to a complete stop in 4.5 seconds.
What is the average force that the brakes must exert during braking?

So far i have the acceleration (-200m/sec) and the mass (1326.5kg) I'm not sure if those are right, but besides that I am at a loss at what to do next.

 

[hotvette]

Welcome to PF!

1. Show us how you arrived at the value for acceleration (though you used units of velocity)

2. Which of Newtons's laws might be applicable here?