Microeconomics -If the tax multiplier is -1.5 and a $200 billion tax increase

If the tax multiplier is -1.5 and a $200 billion tax increase is implemented what is the change in GDP holding everything else constant? (Assume the price level stays constant.)Suppose real GDP is currently $12.5 trillion and potential real GDP is $13 trillion. If the president and the Congress increased government purchases by $500 billion what would be the result on the economy?