The numbers 3,5,7, a, and b have an average (arithmetic mean) of 15 . What is the average of a and b ?

**Answer Choices**

A. 0

B. 15

C. 30

D. 45

E. 60

The numbers 3,5,7, a, and b have an average (arithmetic mean) of 15 . What is the average of a and b ?

**Answer Choices**

A. 0

B. 15

C. 30

D. 45

E. 60