Atrain starts from rest and accelerates uniformly, until it has traveled 3.7 km and acquired a velocity of what is the acceleration of the train during this time?

The train's average acceleration during this time is

         (7.4 km) / (the time taken)² .

The final velocity is not given in the question ... there's a
place for it, but the number disappeared.  In order to
answer the question, we need to know either the final
velocity or else the time taken by the story.