I need to optimize a problem using excel solver?

My professor did not explain solver at all, and just told us to youtube videos if we had any issues. I have no idea how to even get started. The questions involves 4 methods to purify water. The 4 methods each purify a certain amount of bacteria, viruses, parasites, and organics. The treatments each cost a different amount. I need a method to solve the problem in the cheapest way and reach a minimum standard of purification. For example; Chlorine purifies Bacteria 4, Viruses 4, Parasites 0, and Organics 0.1, while the other techniques have different values. My goal is to reach a minimum of Bacteria = 6, Viruses = 4, Parasites = 3, and organics = 1. The cost to use Chlorine is $30,000, and the others each have different costs. Any help on how to get started would be great.