1 hour is equivalent to 60 minutes
3/4 hours is - 60 minutes x 3/4 = 45 minutes
3 hours are equivalent to 60 minutes/hr x 3 hr = 180 minutes
it takes Cindy 45 minutes to complete a puzzle
so it takes her 45 minutes for - 1 puzzle
then in 180 minutes she can make - 1/45 x 180 = 4 puzzles
in 3 hours she can complete 4 puzzles
