You can see how many puzzles are in a Journey by going to Curriculum > All Learning Objectives. The number of puzzles and objectives will appear next to each grade. You can select a grade to see how they're broken our between Journey, Bonus, Challenge, and Optional objectives.
Also check out How many puzzles can I expect my students to complete each week? and How is Percent Progress Calculated?
Note: MIND regularly analyzes and enhances puzzles so the feedback animations are as effective and streamlined as possible. For this reason, Puzzle counts may change from time to time.