1) He can’t go out because he has to study for his exam.

=> If he didn’t have to study for his exam, he could go out.

2) She is lazy so she can’t pass the exam.

=> If she weren’t lazy, she could pass the exam.

3) He will pay me tonight; I will have enough money to buy a car.

=> If he pays me tonight, I will have enough money to buy a car.

4) He smokes too much; that’s why he can’t get rid of his cough.

=> If he didn’t smoke too much, he could get rid of his cough.

5) She is very shy, so she doesn’t enjoy the party.

=> If she weren’t shy, she would enjoy the party.