[SOLVED] Diffucult intro to calculus problem

Coming from Calculus 1, section on introduction to differential equations.

Corruption in Government-

The number of people implicated in a certain major government scandal increases at a rate jointly proportional to the number of people already implicated and the number involved who have yet been implicated. Suppose 7 people were implicated when a Washington newspaper first made the scandal public, that 9 more were implicated over the next 3 months, and that another 12 people were implicated during the following 3 months. Approximately how many people are involved in the scandal?

[Warning: This problem will test your algebraic ingenuity!]

Anyone have any clues on how to begin this bad boy?