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.