The position of a pinewood derby car was observed at various times; the results are summarized in the following table. Find the average velocity of the car for (a) the first second, $(b)$ the last 3 s, and $(c)$ the entire period of observation.
$$\begin{array}{lllllll}\hline t(s) & {0} & {1.0} & {2.0} & {3.0} & {4.0} & {5.0} \\ \hline x(\mathrm{m}) & {0} & {2.3} & {9.2} & {20.7} & {36.8} & {57.5} \\ \hline\end{array}$$