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

Ex Input:
Problem: of 30 applicants for a job , 9 had at least 4 years ' experience , 18 had degrees , and 3 had less than 4 years ' experience and did not have a degree . how many of the applicants had at least 4 years ' experience and a degree ?

Ex Output:
10


Ex Input:
Problem: the dimensions of a room are 25 feet * 15 feet * 12 feet . what is the cost of white washing the four walls of the room at rs . 7 per square feet if there is one door of dimensions 6 feet * 3 feet and three windows of dimensions 4 feet * 3 feet each ?

Ex Output:
s . 6342


Ex Input:
Problem: a father is now 3 times as old as his son . 8 years back , he was 4 times as old as his son . the age of the son ( in years ) is

Ex Output:

24