The correct answer to this open question is the following.
The decision-making process of how much money should be in our economy relies on the Federal Reserve that serves as the central bank of the United States. The Fed, as is commonly known, is the institution in charge of deciding the money supply in the United States economy. What the Fed does is that it uses open market operations to print or create money. Then, with new money, the Fed purchases securities. It also considers to create reserves of money, in case it is further needed.