To solve this problem, we first make a chart that shows the spending pattern of $90 million over 23 years.
$90 million at 11% = [math]\frac{90 \times 1.11^{23}}{100}=903.478[/math]. The future worth at the end of the 23-year is approximately $903,478.
Since the problem does not provide a standard amount of time that people usually use to measure interest rates, we can infer that this rate should be 10% per year.
Using 10% per year instead of 11%:
$90 million at 10% = [math]\frac{90 \times 1.10^{23}}{100}=897.507[/math]. The future worth at the end of the 23-year is approximately $897,507.
Since the total amount that was spent on development over a period of 23 years is $90 million and the answer in our problem has to be in millions, we have to adjust the amount.
$90 million x 100 = $9 billion. The future worth at the end of the 23-year is approximately 9 billion dollars.
