SOLUTION: A car travels 168 miles in 3.2 hours. Find the car's rate of speed in miles per hour.

1.  There is no such a notion/conception "the car's rate of speed".

    It is your mistake using this terminology.

    In opposite, there is the term "the car's rate".


    The term "the car' speed" is also acceptable. 

    But not "the car's rate of speed".  It is not acceptable.



2.  The car's rate =  =  miles per hour.

    Calculate it.