The task is to generate the correct answer for a given math problem.

Ex Input:
Problem: if 1 / ( x + 4 ) + 1 / ( x - 4 ) = 1 / ( x - 4 ) , what is the value of x ?

Ex Output:
4


Ex Input:
Problem: an aeroplane covers a certain distance of 670 kmph in 6 hours . to cover the same distance in 6 1 / 4 hours , it must travel at a speed of

Ex Output:
643


Ex Input:
Problem: a can do a piece of work in 4 hours ; b and c together can do it in 3 hours , while a and c together can do it 2 hours . how long will b alone take to do it ?

Ex Output:

12 hours