1. If you put on your glasses, you would see better. If you had put on your glasses, you would have seen better.
2. If no one came to help, we would be obliged to do the work ourselves. If no one had come to help, we would have been obliged to do the work ourselves.
3. If I wasn't too busy, I would go to the concert. If I hadn't been too busy, I would have gone to the concert