Suppose a student carrying the virus returns to an isolated campus of 1000 students. It is assumed that the rate at which the virus spreads is proportional not only to the number yof infected studentsbut also to the number of students not infected. It was observed that after 4 days . a)Write the DE modeling the number of infected students. b)Draw the phase line and sketch several graphs of solutions in the ty-plane. c)Determine the number of infected students after 6 days. y(4)=