12.12 Process fluid is heated in a series of three stirred tank heaters of the same size. The outlet temperature is measured and controlled to set point by manipulating the heating rate of the first heater. The heating rates of the second and third heaters are constant. Assuming very fast sensor and actuator dynamics, the control system is represented in block-diagram form as follows. (b) If the controller is P only, the set point is the same at all times, and the feed temperature T0 undergoes a step change of size M, calculate the offset as a function of the controller gain. What is the smallest feasible offset