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

Problem: the smallest value of n , for which n + 2 is not a prime number , is
2,4

Problem: how many numbers are divisible by both 2 and 3 up to 300 ?
50

Problem: the ratio between the present ages of a and b is 3.5 : 3 respectively . the ratio between a ' s age 4 years ago and b ' s age 4 years hence is 1 : 1 . what is the ratio between a ' s age 4 years hence and b ' s age 4 years ago ?

15 : 11