3. I didn’t see the signal, so I didn’t stop.

⇒ Had ___ I seen the signal I would have stopped___

4. If I were rich, I could afford to buy an expensive car.

⇒ Were ___I rich and I could afford to buy an expensive car___

5. If I were you, I would tell him the truth.

⇒ Were ___I you, I would tell him the truth___