-He can't go out because he has to study for his exam
=> if he didn't have to study for his exam
-she is lazy so she can't pass the exam
=>If she weren't lazy, she could pass the exam
-he will pay me tonight because i will have enough money to buy a car
=>If he pays me tonight, i will have enough money to buy a car
-she is very shy , so she doesn't enjoy the party
=> If she weren't very shy, she would enjoy the party
-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