A Tank Holds $1000$ Gallons of Water, Which Drains from the Bottom of the the Bottom

A tank holds $1000$ gallons of water, which drains from the bottom of the tank in half an hour. The values in the table show the volume V of water remaining in the tank (in gallons) after $t$ minutes. If $P$ is the point $(10,275)$ on the graph of V, fill the table with the slopes of the secant lines $\mathrm{PQ}$ where Q is the point on the graph with the corresponding $t$ . $\begin{array}{|c|c|c|c|c|c|c|}\hline t \text { (min) } & 5 & 10 & 15 & 20 & 25 & 30 \\\hline V \text { (gal) } & 686 & 481 & 263 & 171 & 22 & 0 \\\hline\end{array}$ Enter your answer to two decimal places.
$\begin{array}{|c|c|}\hline t & \text { Slope } \\\hline 5 & \\\hline 10 & \\\hline 20 & \\\hline 25 & \\\hline 30 & \\\hline\end{array}$