Assume N(t) denotes the size of a population at time t and that N(t) satisfies the equation:
dN/dt = 3N (1- N/20)
Let f(N) = 3N (1-N/20), N> (greater than or less) 0. Graph f(N) as a function of N and identify all equilibria (that is, all points where dN/dt =0).