Candace asked 100 students which crisp flavour they liked best out of
ready salted, cheese and onion or salt and vinegar.
42 of the students are boys.
17 of these boys liked cheese and onion the best.
15 girls liked ready salted best.
23 out of the 39 students who like salt and vinegar best are girls.
Work out the number of students who like ready salted best.