[IKE]

"I'm provided with both the initial and final distances, along with the mile:fps change in velocity ratio for these altitudes."

Sounds like to me it is a little more simple than they are making it out to be. If you have the ratio, you can figure out the initial and final velocities from that ratio table. Change in velocity is just the difference. Now if you need to calculate a rate of change of velocity (constant deceleration), then the equation your friends gave would be correct.

I am not a Rocket scientist, but I was a Physics tutor in College. Without the exact details of the problem, that is about all I can help. If you would like some further assistance, feel free to PM me and I can discuss further.