Exercise 2. 'Water
in bathtub' is the stock, measured as a volume of water, in L. The bath initally holds 100 L of water. The bath receives water from the taps ('Variable inflow
from tap', in
L/min) and loses water to the drain ('Constant outflow to drain', in
L/min). 'Twiddling the taps' gradually ramps the inflow between a minumum of 0
L/min and a maximum of 60 L/min within each 5 minute (300 second) intervals. The outflow
remains constant at 30 L/min.