A decrease in the money supply. AD falls since the money supply decreases. A tax on credit card purchases. AD stays the same. As per the notes, if spending and the money supply stay the same, this just means that the government borrows less.
AD stays the same.
As per the notes, if taxation and the money supply stay the same, this just means that the government borrows less. That makes more loanable funds available to non-government borrowers, balancing out the fall in government spending. If the government borrows less, the demand for loanable funds falls. Interest rates thus tend to fall. For the Fed to prevent this fall, it must reduce the money supply.