The average age of the 40 members of a computer science camp is 17 years. There are 20 girls, 15 boys, and 5 adults. If the average age of the girls is 15 and the average age of the boys is 16 , what is the average age of the adults?
Answer Choices
A. 26
B. 27
C. 28
D. 29
E. 30