1. 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.
\begin{tabular}{|c|c|c|c|c|c|c|}
\hline\( t(\mathrm{~min}) \) & 5 & 10 & 15 & 20 & 25 & 30 \\
\hline\( V(\mathrm{gal}) \) & 694 & 444 & 250 & 111 & 28 & 0 \\
\hline
\end{tabular}
(a) If \( P \) is the point \( (15,250) \) on the graph of \( V \), find the slopes of the secant lines \( P Q \) when \( Q \) is the point on the graph with \( t=5,10,20,25 \), and 30 .
(b) Estimate the slope of the tangent line at \( P \) by averaging the slopes of two secant lines.
(c) Use a graph of the function to estimate the slope of the tangent line at \( P \). (This slope represents the rate at which the water is flowing from the tank after 15 minutes.)
