#### Explanation:

As I recall

• The reserves are a portion of the balance banks must have on hand as cash. A 10% reserve ratio on $3 million open market purchase would imply $0.3 million would need to be added to the reserves.
• The change in money supply is calculated as the change in reserves times the money multiplier. In this case, with a money multiplier of $10$, the change in money supply would be $0.3 million times $10$or $3 million.