Hello!
To find out how long the movie was, you'll need to add some numbers. First, you'll add 15 to 7:45 giving you a time of 8:00. Next, you'll add an hour or 60 minutes to 8:00 to get 9:00, Lastly, you'll need to add 30 minutes to 9:00 to get a time of 9:30. Now to see how long the movie was, add all the 3 numbers that were added to the times
15+60+30
Once you've added up, the movie would be 105 minutes or 1 hour and 45 minutes.
I hope this help!