what is exact meaning of "in which " and "by which"??

sentence:
1.The American economic system is organized around a basically private-enterprise, market-oriented economy in which consumers largely determine what shall be produced by spending their money in the marketplace for those goods and services that they want most. (puff puff, out of breath reading without a pause! :D )
2. An important factor in a market-oriented economy is the mechanism by which consumer demands can be expressed and responded to by producers.

A. First sentence use "in which ", B.second sentence use "by which ", but i can not find verb that can match "in" and "by", i want to know the meanings, but i can not find answer even though through search google. Can some one help me??

A preposition links to other words, not necessarily verbs.

A. in which refers to economy. It's just a relative pronoun with a preposition, and the prepositon could go at the end

B.'mechanism by which' similarly by links to mechanism, and is the same grammar.

You don't need to look for the verbs determine, express