Adeline started reading a book at $5:45$ p.m. and finished at $7:45$ p.m. How long did Adeline spend reading her book? Your answer should be: • an integer, like $6$ • an exact decimal, like $0.75$ • a simplified proper fraction, like $3/5$ • a simplified improper fraction, like $7/4$ • a mixed number, like $1\;3/4$ hours