Oil leaked from a tank at a rate of $r(t)$ liters per hour. The rate decreased as time passed and values of the rate at 2-hour time intervals are shown in the table. Find lower and upper estimates for the total amount of oil that leaked out.
$$
\begin{array}{|l|c|c|c|c|c|c|}
\hline t(\mathrm{~h}) & 0 & 2 & 4 & 6 & 8 & 10 \\
\hline r(t)(\mathrm{L} / \mathrm{h}) & 8.7 & 7.6 & 6.8 & 6.2 & 5.7 & 5.3 \\
\hline
\end{array}
$$