Some analysts say that Rockefeller's net worth was economically equivalent to approximately $x billion today. This figure is arrived at in a particular way. First, his net worth in 1937 is calculated as a percentage of total U.S. GDP in 1937. That percentage is then multiplied by the current level of GDP to arrive at the equivalent figure in current dollars. You can find the relevant GDP figures at http://research.stlouisfed.org/fred2/data/GDPA.txt. Compute x. (Show your calculations.) (5 points)