The ages of a group of executives attending a convention are uniformly distributed between 35 and 65 years. If the random variable $X$ denotes ages in years, the probability density function is as follows:
$$
f(x)= \begin{cases}1 / 30 & \text { for } 35<x<65 \\ 0 & \text { for all other values of } x\end{cases}
$$
a. Graph the probability density function for $X$.
b. Find and graph the cumulative distribution function for $X$.
c. Find the probability that the age of a randomly chosen executive in this group is between 40 and 50 years.
d. Find the mean age of the executives in the group.