Suppose an economy has a national debt of $10 billion, and the average interest rate on this debt is currently 3%. Its GDP is $20 billion. Suppose that next year one of two events occurs: (1) GDP and interest rates stay the same, but the economy adds $2 billion to its national debt. (2) GDP and the national debt stays the same, but interest rates increase to 4%. Which of these two events would increase the interest rate burden of the national debt more? Show your calculations.