Question

Over a span of 6.0 seconds, a car changes its speed from 89 km/h to 37 km/h. What is its average acceleration in meters per second squared (m/s2)

Answer 1

First, you should convert the initial and final velocities from km/h to m/s.  You should end up with Vi= 25m/s and Vf=10m/s (both rounded).
Now, you can use the equation Vf=Vi+A(t)
Rearrange it to A is isolated: A= Vf-Vi/t
A=(10-25)/6
A=-2.5m/s^2