The Average Value of Y = H(x)equals a for 0 $\le$

Multiple Choice

The average value of y = h(x) equals a for 0 $\le$ x $\le$ 5, and equals b for 5 $\le$ x $\le$ 15.What is the average value of h(x) for 0 $\le$ x $\le$ 15?

A) $\frac{a+b}{2}$
B) $\frac{a+2 b}{3}$
C) $\frac{a+b}{15}$
D) $\frac{a+2 b}{15}$