Problem 18, i’m not sure how to do it and need help.

The Sewage and Farm runoff are both entering the ocean in the largest amounts due to overpopulation, when a city gains more people, the farms need to produce more, while the smaller farmers' markets are trailed behind during this process, the larger companies using mass production take over, creating waste that leads to the ocean. When this happens, and more people are coming in, they create more waste, from washing hands, dishes, showers, to using the restroom, it all leads into one large sewage system, which leads out to the ocean.

It's a big cycle, all leading to the demise of the ocean