I am just learning how to do this for my calculus class so forgive me for being so ignorant, but I am trying.

For the problems I am doing, these two formulas are being used:

v(t)= v(sub zero) + at

s(t) = s(sub zero) + v(sub zero)t + .5at^2

I'm having a lot of trouble with applying these. For example, the current problem I am on says:

"Spotting a police car, you hit the brakes on your new Porsche to reduce your speed from 90mi/h to 60mi/h at a constant rate over a distance of 200 feet. (88ft/s=60mi/h)

Find acceleration in ft/s^2"

I need to understand which formula is appropriate for various situations. I realize:

initial velocity= 132ft/s

final velocity= 88ft/s

initial displacement=0ft

final displacement= 200ft

I have no idea how to find time to solve for acceleration, so both formulas seem useless to me.

If someone could explain these formulas and help me on this current problem, I would really appreciate it. I've been on this same problem for 3 hours and have gotten nowhere.