instruction:
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: a cistern is normally filled in 6 hours but takes two hours longer to fill because of a leak in its bottom . if the cistern is full , the leak will empty it in ?
answer:
24

question:
Problem: a square mirror has exactly half the area of the rectangular wall on which it is hung . if each side of the mirror is 21 inches and the width of the wall is 28 inches , what is the length of the wall , in inches ?
answer:
31.5