Question: What are three ways to burn 100 calories in less than one hour?
Option 0: Walking for half an hour, even slowly will burn 100 calories. Walking up or down stairs will burn 100 calories in about 15 minutes. Raking leaves will get you there in 20 minutes.
Option 1: It's best not to worry about burning calories, just don't eat so much high calorie foods. Even worrying about weight loss will eventually burn  an extra 100 calories especially if you wring your hands and pace while doing so.
Answer: 0