It is a simple sentence.
A simple sentence contains one independent clause - which is the case with sentence 7. There is one subject (they) and one verb (rule), which means that it is a simple sentence (because of one verb only). A dependent clause wouldn't be able to stand on its own, and sentence 7 obviously can, which is why it is not dependent.
I think it would be the one from paragraph 4, it shows laura has overheard what they were talking about and her mood changes and feels hurt
1/7 of 42 is 6
2/3 of 42 is 28
42-6-28=8
8/42=4/21
4/21
