The hidden question the sum of three different numbers is 18. If every number is a prime number, what are the three numbers

For these types of questions you have to think it out. List the prime source lower than 18. 2,3,5,7,11,13,17. Then take a look and test some pairs.

Eventually you'll find that 11, 5, 2 is a solution.

5, 11 and 2 are all prime numbers which add together to create 18.

5+11=16+2=18