If money is invested at r percent interest, compounded annually, the amount of the investment will double in approximately $$\frac{70}{r}$$ years. If Pat's parents invested $5,000 in a long-term bond that pays 8 percent interest, compounded annually, what will be the approximate total amount of the investment 18 years later, when Pat is ready for college?
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A$20,000
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B$15,000
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C$12,000
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D$10,000
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E$9,000