As a female, 5'6" and 140 lbs, I burn about 700 calories in a 1 hour spin class. This number will be different for everyone since people push themselves to different limits and use different resistance levels.
about 288 calories
20 pounds.. mabye
It depends on what you are doing. Different exercises (or lack therof) will bunr very different amounts of calories in an hour and a half.
200 if you didnt snack during or after
200-400 calories