The task is to generate the correct answer for a given math problem.
--------
Question: Problem: a train running at the speed of 40 km / hr crosses a pole in 9 seconds . what is the length of the train ?

Answer: 100 meter


Question: Problem: two trains of length 100 meters and 200 meters are 450 meters apart . they are moving towards each other on parallel tracks , at speeds of 90 km / h and 72 km / h . after how many seconds will the trains meet ?

Answer: 10


Question: Problem: the average of 9 observations was 8 , that of the 1 st of 5 being 10 and that of the last 5 being 8 . what was the 5 th observation ?

Answer:
18