Ответ:

1. If you had come, you would have met my friends from Hungary.

2. He wouldn't have helped you if you hadn't helped him.

3. If you hadn't helped me, I would n't have passed the exam yesterday.

4. ...what I will do with the money if I win the lottery.

5. She will be in trouble with her father if she fails the exam.

6. If Mark trained harder, he would be a good runner.