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

Problem: the least number which should be added to 1789 so that the sum is exactly divisible by 5 , 6 , 4 and 3 is ?
11

Problem: a and b together can complete work in 6 days . a alone starts working and leaves it after working for 4 days completing only half of the work . in how many days it can be completed if the remaining job is undertaken by b ?
12

Problem: two tains of equal lengths take 10 seconds and 15 seconds respectively to cross a telegraph post . if the length of each train be 120 metres , in what time ( in seconds ) will they cross each other travelling in opposite direction ?

12