Answer:
1140 trees
Explanation:
Since the woods have 20 trees per square mile, we can find the number of trees surrounding Rapunzel's house by multiplying 20 by 57:
# of trees = 20 * 57
# of trees = 1140
Thus, there are 1140 trees surrounding Rapunzel's house.
You can further prove this face with division:
1140 trees / 57 square miles reduces to 20 trees / 1 square mile, proving that our answer is correct.