How much exercise do you need to do to burn off 55 grams of fat?

Remember firstly that you're always burning calories, even when you aren't exercising. Secondly, remember that not all the calories you burn during exercise are from fat, as some are from carbohydrates, and a few are from protein. 55 grams of fat are roughly 500 calories. So to do exercise which burns off the number of calories found in 55 grams of fat, you'd need to do... well, some exercise which registers 500 calories as being burned. That depends on the intensity of your exercise, along with your body composition/mass (larger people doing the same activity would burn more calories, as they have to move a greater mass through this activity). That could be 45 minutes of intense biking or whatever else tickles your fancy. Again, remember that you're always burning calories, even just sitting around. The average person would burn around 1000-1500 calories a day just lying in bed all day. It's not consuming too many grams of fat which makes a person gain weight, it's consuming more calories in a day than one expends, whether it's from fats, carbohydrates or protein.