We're given the velocity at two points, and the time between the mentioned two points.
What we'll be calculating is the average acceleration (not to be confused with instantaneous acceleration).
Given two points, lets call them initial and final, the average acceleration is calculated as:
[tex]a= \frac{v_f-v_0}{t}[/tex]
In which [tex]v_f[/tex] is the final velocity (in your problem equal to 1m/s), [tex]v_0[/tex] is the initial velocity (in your problem equal to 16 m/s), and [tex]t[/tex] the time between two points (in your problem equal to 2s).
So, we plug-in our known values:
[tex]a= \frac{v_f-v_0}{t}= \frac{1-16}{2}=-7.5 [/tex]
The answer is -7.5m/s^2.
