I don't know how to solve this, can I get a little help?
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Explanation:
Acceleration is the change in velocity over change in time.
a = Δv / Δt
So it is the slope of the line of a velocity vs. time graph.
a = (10 m/s − 40 m/s) / (12 s − 0 s)
a = -2.5 m/s²