Find the acceleration of the following taxi. the taxi initially starts at 0 mph. after driving for 30 seconds the final velocity of the taxi is 230 mph.

Since there isn't a word about the direction of the taxi's
motion, we're in no position to talk about 'velocity', so we'll
just talk about 'speed'. 

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

                       =         (230 mph)      /      (30 sec)

                       =                        23/3        mile / hour-sec .

This is just a hypothetical question, made up for Physics practice ...
so I'm not too worried about the taxi's final speed of 230 mph. 
There's no way the Police are going to catch him, even in their
helicopter, so he's safe for a while. 

What DOES bother me is that ugly unit for acceleration ...
mile / hour-second.  It's a perfectly valid unit of acceleration,
having the dimensions of  [distance / time²], but it's not one
that anybody has a feeling for, so we can't relate to it and we
don't know what it means.  We need to change it to a unit that
we understand.  That's not hard to do.

 (230 mile/hour-sec) x (1,609 meter/mile) x (1 hour/3,600 seconds)

  =      (230 x 1,609 / 3,600)   meters/second²

  =                   102.82  m/s²   =   10.5 G's  !

That's a problem.  The taxi is pulling 10.5 G's, the police helicopter
is in hot pursuit, the driver is passing out, and the taxi is almost
certainly falling apart around him.  Meanwhile, from the back seat,
the passenger is yelling "Check your data!".  CHECK YOUR DATA !