I'm pretty sure it needs to be solved through row echelon, but I've tried multiple times and can't seem to work this thing out..can anyone help me?

Problem:

Find the position equation for s=(1/2)at^2+vt+so

At t=1 second, s=128 feet

At t=2 seconds, s=80 ft.

At t=3 seconds, s=0 ft.

Please and thank you if anyone helps! :x