What is the Average Acceleration of a Car Striking a Tree at 90 km/h?

[Gustason]

Homework Statement

A car traveling at 90 km/h strikes a tree. The front end of the car compresses and the driver comes to rest after traveling 0.86 m. What was the average acceleration of the driver during the collision?
Express the answer in terms of "g's," where 1.00g = 9.81 m/s2

Homework Equations

a = Change in X / Change in T
Change in X = vf + vi / 2 * t

The Attempt at a Solution

I should mention that this is all done via a website and we are allowed a certain amount of leeway with rounding. I'll explain why this may or may not be important in the next few lines.
I've found the average acceleration which is -363.37 (this was accepted as the correct answer) but when I divide it by 9.81 to get -37.05 g's the answer is not accepted. I'm thinking that perhaps I made a mistake in the first part of the problem and that is influencing what I get for the g's

 

[Rake-MC]

What is the answer listed in the book?

 

[Gustason]

Well I don't have the book so I don't know. Like I said in my post, this is all submitted online, I'm only told if my answer was accepted or if it wasn't. I don't know what the answer key says.