Final answer:
Lily spent 1 hour and 45 minutes watching the movie.
Step-by-step explanation:
To find out how much time Lily spent watching the movie, we need to determine one-fourth of the movie's length. The movie is 3 and one-half hours long, which is equivalent to 7 halves. So, one-fourth of the movie is 7/4 or 1 3/4 hours. We can simplify this as 1 hour and 45 minutes. Therefore, Lily spent 1 hour and 45 minutes watching the movie.