The weather was bad so we didn't go camping yesterday. => If the weather hadn't been bad, we would have gone camping yesterday.

You didn't phone us so we didn't get there in time. => We would have gotten there in time if you had phoned us.

I wasn't able to help you because you didn't explain the problem to me. => I might have been able to help you if you had explained the problem to me.

They weren't listening carefully so they didn't understand what she was saying. => They might have understood what she was saying if they had been listening carefully.

You took me to your friend's party and I met Hung. => If you hadn't taken me to your friend's party, I wouldn't have met Hung.

If you don't wear a helmet, you can't ride your bike. => Unless you wear a helmet, you can't ride your bike.

I would visit my grandpa, but it's raining. => If it wasn't raining, I would visit my grandpa.