The position of an object moving vertically along a line is given by the function $s(t) = -4.9t^2 + 30t + 18$. Find the average velocity of the object over the following intervals.\
a. $[0, 1]$ \
b. $(0, 4)$ \
c. $[0, 7]$ \
d. $[0, h)$, where $h > 0$ is a real number\
a. The average velocity is $oxed{}$ (Simplify your answer.)\
b. The average velocity is $oxed{}$ (Simplify your answer.)\
c. The average velocity is $oxed{}$ (Simplify your answer.)\
d. The average velocity is $oxed{}$