If you mean the penny's value doubles every day, then do this: \(0.01*{2}^{30}\)
Since \(0.01*{2}^{30}\) = 10 737 418.24, the penny would be worth that much in 30 days.
However, you have not specified what the exponent is. So, just replace the base of \({2}^{30}\) with whatever your exponent is. If the penny's value x10 every day, then change it to: \({10}^{30}\)
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