Answer:
a) An expansionary monetary policy which increases the economy's money supply, requires that the FED purchases securities. This way the FED will inject money into the economy.
b) we must first determine the money multiplier = 1 / reserve ratio = 1 / 20% = 5. If the FED wants to increase the money supply by $40 million, it must inject $40 million / 5 = $8 million. This way the $8 million will turn into $40 million.