1. the water is so dirty that he can't bathe his eyes
-The water is not clean enough for him to bathe his eyes 
2.I gave up smoking ten years old
-I used to smoke ten years ago 
3. John used to go on bare foot when he was a little boy.
-John often went on bare foot when he was a little 
4.he doesn't play tennis as well as he used to.
- He used to play tennis very well
5. I walked to scholl in 20 minutes
- It took me 20 minutes to walk to school 
6.When i was a child, I was afraid of ghost.
- I used to be afraid of ghost 
8. It took him an hour to solve that exercise
- He solved exercises in an hour