Antonette gets 70 \% on a 10 -problem test, 80 \% on a 20 -problem test and 90 \% on a 30 -problem test. If the three tests are combined into one 60 -problem test, which percent is closest to her overall score?
Answer Choices
A. 40
B. 77
C. 80
D. 83
E. 87