1. If he is not very busy, he will help you.
If he was not very busy, he would help you.
If he had not been very busy, he would have helped you.
2. If they finish their work quickly, they will go home early.
If they finished their work quickly, they would go home early.
If they had finished their work quickly, they would have gone home early.
3. If the pric on this product goes up, nobody will buy it.
If the pric on this product went up, nobody would buy it.
If the pric on this product had gone up, nobody would have bought it.
4. If the rain stops, the girls will go for a walk.
If the rain stopped, the girls would go for a walk.
If the rain had stopped, the girls would have gone for a walk.