The average age of three boys is 15 years and their ages are in proportion 3:5:7. What is the age in years of the eldest boy?	Options.
A) 6
B) 9
C) 16
D) 4
E) 21
3x + 5x + 7x = 45   x =3   7x = 21   Answer:21
<result>E</result>
The average age of three boys is 15 years and their ages are in proportion 3:5:7. What is the age in years of the eldest boy?