Trying to find displacement using velocity and acceleration

[mrsconfused]

Homework Statement

A train traveling at a velocity of 60.0 m/s is slowed down at a uniform rate of 1.25 m/s2. How far will it travel before its velocity is 1/2 its original value?

Homework Equations

v² = v_o² + 2ad

The Attempt at a Solution

I first need to isolate my variable, so 'd'. In which case, I believe the equation would then look like 'd=v_o² $\div$ v²+2a. Filling in this equation with the numbers then looks like: d=60m/s²$\div$30m/s²+2(-1.25m/s²). But when I calculate it all out I'm left with d=-0.5m/s². This does not make any sense though; it's not possible for the train to travel a negative amount of distance. And also, isn't displacement measured in units of length and not time? I can't figure out how to get rid of the seconds. Needless to say, I am very confused. Thanks in advance.

 

[haruspex]

I believe the equation would then look like 'd=v_o² $\div$ v²+2a.

I don't. Try that manipulation again. If you're still stuck, post your detailed working.