Question

The graph below shows the water level of a tank that is emptying over time.

Answer 1

From inspecting the graph, you can identify the y-intercept and the slope of the line shown.

The y-intercept is 200 gallons.
The slope is 

             75-200
    m = ------------- = -12.5 gallons/minute
               10 -  0

Thus, y = 200 gallons - [12.5 gallons/minute ]t

To answer the 2nd question, let t = 12 minutes and calculate y(12).

To determine how long it wld take to empty the tank, set the above formula equal to zero and solve the resulting equation for t.