OK, just to make sure I'm getting this, teach', can ya grade my homework here?
(1977) Three Act Structure:
Main Character = Luke Skywalker
Inciting Incident = Luke hears part of Leia's message, "Help me, Obi-wan Kenobi. You're my only hope."
Plot Point #1 = Luke finds Uncle Owen and Aunt Beru with their flesh burned off. There's no going home.
Dramatic Question = Will Luke be able to help the Princess? (See below.)
First Culmination = The Millennium Falcon arrives at Alderaan's position.
Midpoint = But Alderaan is destroyed, and the Millennium Falcon is brought aboard the Death Star.
Plot Point #2 = Ben is struck down by Vader.
Climax = Luke destroys the Death Star.
The exact wording of the Dramatic Question, "Will Luke be able to help the Princess?" is from dialog of Ben's, right after Ben and Luke hear the whole holographic message:
Ben: I need your help, Luke. She needs your help. I'm getting too old for this sort of thing.
By "help the Princess," it is at first meant two items established more or less unambiguously in the First Act:
1) Deliver R2-D2 to the Princess's father on Alderaan, so that he can
2) Retrieve the plans to the Death Star in R2's memory.
When Luke and Ben find Alderaan destroyed, they see their original plan fall to pieces. Soon after the Midpoint, Luke discovers that the Princess is on board, so helping her now becomes simply:
3) Rescue the Princess.
Once the Millennium Falcon is away from the Death Star after the rescue, Leia reveals the purpose of accessing the plans. It is, as hinted at during the opening crawl and suspected by Taggi [sic] in the First Act, to find a weakness in the battle station. This sets up the climax, by revealing the final condition to helping the Princess:
4) Destroy the Death Star.