A variable R(t), t20 obeys the differential equation dR dt = - 12 (2 R) (eR 1)|R + 1|e-5R+19 (4.1) Determine the equilibrium points of the model, and draw a phase line of the model. Indi the direction of motion in each interval of the phase line. (4.2) State which equilibrium points are stable and which are unstable. (4.3) Analyse, without solving the differential equation, what will happen in the model as t when different starting values of R(0) are used.