Last year, the enrollment at Brown Middle School was 900 students. This year, the enrollment is 720 students. Which of the following statements ocrrectly compares this year's enrollment to las year's enrollment? a
The enrollment increased by 20%
b
The enrollment increased by 80%
c
The enrollment decreased by 20%
d
The enrollment decreased by 80%

Need help plz. Also you an give me an explanation but you dont need too.