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.
(a) If P is the point on the graph of V, find the slopes of the secant lines PQ when Q is the point on the graph with .
(b) Estimate the slope of the tangent line at P by averaging the slopes of two secant lines.
(c) Use the 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.)
(c) Use a graph of the function to estimate the slope of the tangent at line at P.( This slope represent the rate at which the water is flowing from the tank after 15 minutes).
on the graph V , find the slope of the secant line 
when 
is the point on the graph with 
.
