I have a question with 3 parts, I have done the first 2 parts but i cannot make sense of the last part and was wondering if someone could please help me?

Q: 75 pupils, 48 pupils like ready salted, 35 like cheese & onion

i) if 7 pupils do not like either flavor, how many like both?

A: 15

ii) *what is the greatest possible number of pupils who could like both?

A: 35

**what is the smallest possible number of pupils who could like both?

A: 8

Now this is the part that i cannot figure out:

The number of pupils who like both is twice the number who do not like either;

iii) what fraction of the pupils who like ready salted do not like cheese & onion?