Translate the English statement into a differential equation. Be sure to specify what your variables are.
The number of bunnies in the forest is increasing at a rate proportional to the number of bunnies there already.
The two variables are the number of bunnies B and the time t. The statement
The number of bunnies is increasing at a rate proportional to the number of bunnies can be condensed into the statement B is increasing at a rate proportional to B. As a differential equation,
where k is the constant of proportionality.