Let $w$ be the number of worms (in millions) and $r$ the number of robins (in thousands) living on an island. Suppose $w$ and $r$ satisfy the following differential equations, which correspond to the slope field in Figure 9.44.
(FIGURE CANNOT COPY)
For the case discussed in Problem $12,$ estimate the maximum and the minimum values of the robin population. How many worms are there at the time when the robin population reaches its maximum?