Adragster going at 5 m/s north increases its velocity to 23 m/s north in 4 seconds. what is its acceleration during this time interval?

To my recollection vf=vi+at
23m/s=5m/s + a (4s)
get the like units together
23m/s - 5m/s = a (4s)
18m/s = a (4s)
divide each side by 4 to find a
18m/s / 4s = 4.5m/s

I don't know how to do the up arrow to square any of the m/s.

Answerwavelength;

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