1. My brother didn't leave the car keys, so I couldn't pick him up at the station.

=> If my brother had left the car keys, I would have picked him up at the station.

2. If Susan Hadn't eaten 4 cream cakes, she wouldn't have felt sick

 

1.My brother didn't leave the car keys, so I couldn't pick him up at the station.

=> If my brother had left the car keys, I would have picked him up at the station.
2.Susan felt sick because she ate four cream cakes.

=>If Susan hadn't eaten four cream cakes, she wouldn't have felt sick.
3.Don't complain any more or they'll sack us
=> If you dont complain any more , they wont sack us
4.He often works overtime.His health is worse and worse
=> If he didn't work overtime so often, his health wouldn't be worse and worse