Each of the following sentences contains a mistake

Exercise 4. Each of the following sentences contains a mistake. Underline it and write the correct answer in the space provided
6. The girl is the most beautiful of the two daughters that she has
 7. Frank plays tennis worse of all the players.
8. She can pronunce English words more correct than she could last term.
9. This summer is hotter and winder than last summer.
10. She is much more intelligent than nam does.