Length of Skid Marks

Homework Statement

A 1000 kg car traveling at a speed of 40 m/s skids to a halt on wet concrete where $$\mu$$k = 0.60. How long are the skid marks?

Homework Equations

fk = $$\mu$$kN = ma

The Attempt at a Solution

This problem is driving me crazy. Nowhere in the book does it tell you how to do this or even a similar problem. Plus, online, all I can find is how to find the speed once you've found the length of the skid marks! And yes, I tried doing the problem in reverse but the answer never comes out right.

Here is what I've done.

1000 * 9.8 = 9800
9800 *.6 = 5880
acceleration = 5880/1000 = 5.88

0 = 40 + 2 * 5.88 * d
d = 3.4

I know I've done something incredibly wrong here because the answer in the back of the book is 136!

I appreciate the help

a(1000) = 5800