Estimating Car Speed from Skid Marks

[nordqvist11]

Homework Statement

In coming to a stop a car leaves skid marks 92m long on the highway. Assuming a decceleration of 7.00 m/s^2 , estimate the SPEED of the car just before braking.

I have a question though, is my approach ok? You can see my confusion in various parts of my procedures below, I guess it's the fact that it says find speed not velocity.

Homework Equations

Kinematic Equation for constant acceleration.

The Attempt at a Solution

 

[iRaid]

Speed=velocity lol

 

[nordqvist11]

I got -35m/s as my velocity though

 

[lachy89]

Speed is the magnitude of velocity and has no direction.

EDIT: Assuming you are using the formula: v^2=u^2+2as you may need to check what you are using as v and u and be careful of your signs.

0 = u^2 +2as
u^2=-2as

Does that make sense?