13. If my friend and I had enough money, we would buy a house of our own
14. If the weather were better now, we could go for a walk
15. If ticket weren’t expensive, we would visit them in Hanoi.
Unless ticket were expensive, we would visit them in Hanoi.
16.Unless I won a big prize in a lottery, I'd not give up my job.
17.Unless i got up early, i would go to school late
18. If he didn't study hard, he would fail the exam

13. My friend and I don't have enough money, so we will not buy a house of our own.

=>If my friend and I had enough money, we would buy a house of our own

14. The weather isn't better now, so we can't go for a walk.

=>If the weather were better now, we could go for a walk

15. We don't visit them in Hanoi because tickets are expensive.

=>If  ticket weren’t expensive, we would visit them in Hanoi.

=>Unless  ticket were expensive, we would visit them in Hanoi.

16. If I won a big prize in a lottery, I would give my job.

=>Unless  I won a big prize in a lottery, I'd not give up my job.

17. If I didn't get up late, I wouldn't go to school late.

=>Unless  i got up early, i would go to school late