Plot the level response for a tank with constant cross-sectional area of 4 ft² as a function of time for the following sequence of events; assume an initial level of 1.0 ft with the drain open, and that level and outflow rate are linearly related. The steady-state inflow and outflow are initially equal to 2 ft³ / min. The graph should show numerical values of level vs. time.

(a) The drain is suddenly closed, and the inflow remains constant for 3 min (0 ≤ t ≤ 3).
(b) The drain is opened for 15 min, keeping the inflow at 2 ft³ /min, where a steady state is essentially reached (3 ≤ t ≤ 18).
(c) The inflow rate is doubled to 4 ft³ /min for 15 min (18 ≤ t ≤ 33).
(d) The inflow rate is returned to its original value of 2 ft³ /min for 17 min (33 ≤ t ≤ 50).