Atrain is moving 4.82 m/s when it begins to accelerate. after 24.8s it is moving 7.09m/s how far did it move in that time

The train's average speed during that 24.8 seconds is 

                      (1/2) (4.82 m/s + 7.09 m/s)

                =    (1/2)    (11.91 m/s)

                =           5.955 m/s .

Traveling at an average speed of  5.955 m/s  for  24.8 sec,
it covers

                 (5.955 m/s) x (24.8 sec)  =  147.68 meters  .

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