Acar travels 31.2 miles in 36.0 minutes. what is the average speed of the car during this trip, in miles per hour (mph)?

Speed is the distance travelled within a unit time.
in this instance, distance traveled - 31.2 miles 
time taken to travel this distance - 36 minutes
time is given in minutes, we need to convert minutes to hours
60 minutes - 1 hour 
Therefore 1 minute - 1/60 hr
36 minutes -  1/60 hr/minutes x 36 minutes 
                  - 0.6 hr
speed = distance travelled / time taken 
          = 31.2 miles / 0.6 hr
          = 52 mph (miles per hour)
average speed means that on average the car has been travelling at 52 mph speed. within one hour on average the car can cover 52 miles distance.

Earth's rotation cause the global convention current between the equator and the poles