A bookstore sells books in several formats- hardcover, paperback, digital, and audio.
Based on past sales, the table below gives the estimated probabilities that a randomly selected purchase will be of particular types.
$$
\begin{array}{|cccc|}
\hline \text { Hardcover } & \text { Paperback } & \text { Digital } & \text { Audio } \\
\hline 0.16 & 0.36 & 0.40 & 0.08 \\
\hline
\end{array}
$$
If a purchase is selected at random, what is the probability that this purchase is for a book that is
a. digital or audio?
b. not digital?
c. a printed book?