How many calories do you burn when you walk this long?

Yesterday, I walked around the mall for 6 hours straight! I didn't even realize I walked that long! I also went up and down the stairs! I only realized it on the way home, when my feet were keeling me 'coz I wasn't wearing flats! It would have been 7 hours if I didn't rest for 30 minutes to eat my lunch! If you are a 140 lbs girl, and you walk faster than the average person (coz i notice I walk really fast!), how many calories did I burn walking around that long?