Answer:
24 students.
Step-by-step explanation:
Ok, so basically, the question already gave you a number of students that like ready salted. 42 - 17 (cheese and onion) is 25. This means that there is a possibility of 25 more boys on top of the 15 girls who like ready salted. 39 - 23 (total students minus the girls) who like salt and vinegar is 16. 25 - 16 is 9, and add that with 15, you get 24.
