I'm 5'2" and about 144-145 lbs. How many calories do you think I would burn walking about 3.8 miles, with hills involved?

That's really hard to say, because it also depends on how fast you are walking. But, probably something like 400 calories.

Go here:
http://www.healthstatus.com/calculate/cbc

There are lots of calculators on the Web--which may or may not be accurate.