Suppose 125 small business firms are threatened by bankruptcy. If y is the number bankrupt by time t, then 125 - y is the number not yet bankrupt by time t. The rate of change of y is proportional to the product of y and 125 - y. Let 2015 correspond to t = 0. Assume 20 firms are bankrupt at t = 0.

(a) Write a differential equation using the given information. Use 0.002 for the constant of proportionality.
(b) Approximate the number of firms that were bankrupt in 2020, using h = 1 year.