The graph is a line therefore we will calculate the slope of the line because it is the rate of change
[tex]m=\frac{g_2-g_1}{t_2-t_1}[/tex]
where
(0,400)=(t1,g1)
(5,300)=(t2,g2)
we substitute the values
[tex]m=\frac{300-400}{5-0}=\frac{-100}{5}=-20[/tex]
The total capacity of the water tank is 400 gallons, and the rate of change is -20 gallons per hour
