Dave and Julie had to work late so that they would finish their project on time.
If the sentence was rewritten to begin with "Tomorrow night," the next words would be _______.

Because the phrase "Tomorrow night," denotes a point of time in the future, the sentence with these additions should be re-written in the future tense. And the subject of the sentence is "Dave and Julie", which denotes the people carrying out one task, the sentence should be using active voice.
Therefore, the only correct answer is "Tomorrow night, Dave and Julie will have to work late so that they would finish their project on time."