V(t) = k-2t-t^2. [Assume t≥0 and other suitable restrictions]
If 153 gallons remain after 3 min, in how many additional min will the tank empty?
[Suggested Answer: Constant rate implies a linear model]
[Suggested Answer: The coefficient of the quadratic term should be negative since the quantity of water is decreasing. Note that students most often reply "'Because we want graph to open down!" This is insufficient IMO.
[Suggested Answer: Graphically, k is the V-intercept; in the application, k = quantity of water at start or t=0]
[Suggested Answers: Make a t,V(t) table; sketch a graph]