(30,7) was a solution to this graph your equation show that (30,7) actually a solution

compost can be added to topsoil as a:

pesticide

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.