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

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

=>If

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

=>If

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

=>If

=>Unless

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

=>Unless

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

=>Unless

18. Unless he studied hard, he would fail the exam.

=>If