An object is moving at a velocity of 23 m/s. it accelerates to a velocity of 85 m/s over a time of 8.3 s. what acceleration did it experience?

|Acceleration| = (change of speed) / (time for the change)

Change of speed = (speed at the end) - (speed at the beginning)

                           =        (85 m/s  -  23 m/s)  =  62 m/s 

|Acceleration| = (62 m/s) / (8.3 sec) = 7.469... m/s²  (truncated)

I wrote this solution in terms of speed and the absolute value of
acceleration, because there's nothing in the question that suggests
that it has anything to do with velocity ... except the word, used twice.

Velocity and speed are different things.  'Velocity' is not just a big word
that's used in place of 'speed' to make it sound more advanced.  In any
discussion of velocity, the direction of motion must be included. 
Otherwise, speed is all you've got, and velocity is unknown.