b). A research group at USP modelled the spread of the Covid-19 virus. The model that they had depicted that the rate of spread of the Covid-19 virus is proportional to the number of contacts between Covid-19 positive (infected) and negative (noninfected). The people within the zones were moving freely. 1) . Set up the model for the spread of the Covid-19 virus. ii) - Find the equilibrium solutions and indicate their stability or instability. ili). Solve the system model obtained in (1.) above. iv). Find the number of Covid-19 positive people as too and explain what it means. [2+ 2+4+ 2 =10 marks]