1. She doesn't haven't a compurter so he can't work 
->if she had a computer, she could work.
2. I can't help my paren't because I am very busy
->If  I were not very busy, I could help my parents.
3. Study harder or she will fail this exam
->If  she doesn't study harder, she will fail this exam.
4. If we prepare a map a map, he will be last soon
-> Unless we prepare a map, he will get lost soon.

1. If she had a computer, she could work.
2. If I were not very busy, I could help my parents.
3. If she doesn't study harder, she will fail this exam.
4. Unless we prepare a map, he will get lost soon.