Here are the completed sentences using the third conditional:
* If she hadn't missed the bus, she wouldn't have been late.
* I would have had a higher test score if I had completed the project.
* If we hadn't accepted the offer, we wouldn't have experienced such problems.
* If you had driven carefully, you wouldn't have hit the car in front of you.
* I wouldn't have gone there if I had known whose party it was.