Microsoft's stock price peaked at 6118% of its I.P.O. price more than 13 years after the I.P.O. (Source: Bloomberg Financial Markets). Suppose that $10,000 invested in Microsoft at its I.P.O. price had been worth $600,000 (6000% of the I.P.O. price) after exactly 13 years. What interest rate, compounded annually, does this represent?