Answer:
$300 has been reduced from the money supply.
Explanation:
The taxes act as leakage from the circular flow of money. Unless they are spent and injected back as government spending they would be treated as a leakage that has left the circular flow.
Similar effect happens with the savings amount. A saving is a leakage and thus the remaining amount which is $20 after paying for golf clubs and taxes can also be said to have left the circular flow of income and so reducing money supply.
$100 of the original $400 is still left in the flow and money supply as it is still in the checking account after the transaction.
Hope that helps.