You are a logger out in the woods. You find a log that could be spruce or birch. In order to figure out which is, you put the log in a big bucket and find that it displaces 2.7 gallons of water and it weighs 19.8 lbs. Is it spruce or birch? (Density of spruce 0.9 g/cm^3, birch 0.4 g/cm^3)