Question $16$:

The small architectural firm Streefkerk designs and manages various home construction projects. Each project requires on average $18$ months to complete and earns $$60,000$ for Streefkerk. How many active projects do they need to manage $($on average$)$ at any given time to achieve a revenue objective of $$600,000$ per year? $($An active project is one that has started but has not been completed.$)$