90 ft3 of water is added for 1 minute to a tank fed at a rate of 10 ft3/min. The outlet flow rate of the tank is controlled by a valve with resistance R. Write the expression for the change in the liquid level (h'(t) in the tank in the system where the time constant is 1 minute. (Consider that there is a total input of 100 ft3/min to the tank at t=0. The effect given to the tank can be considered as step input) (t=0) 10 ft3/min 90 ft3/min h R ka