Answer :

Set up your data as a fraction.  You are looking to find the total number of miles traveled per hour.  This fraction would look like 2400/48.

You will need to reduce this with the GCF of both numbers.  The GCF for the two numbers is 48.  When you divide 2400 by 48 you end up with 50.  When you divide 48 by 48 it results in 1.  You found the "unit rate" of hours. 

This would then read as: the person/vehicle traveled 50 miles per hour (mph).

Hope this makes sense!  Good luck!
2400 is 8x3x100

48 is 8x3x2

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(8x3x100 miles)/(8x3x2 hours)

=(100 miles)/(2 hours)

=50 mph