(Related to Solved Problem 20.5 on page 683) In an article in the Wall Street
Journal, a professor of financial planning noted the effect of rising prices
on purchasing power: "Today, \(\$ 2,000\) a month seems reasonable [as an income
for a retired person in addition to the person's Social Security payments],
but 40 years from now that's going to be three cups of coffee and a donut."
Suppose that in 2016 three cups of coffee and a donut can be purchased for \(\$
10\). The CPI in 2016 was 240 . What would the CPI have to be in 2056 for \(\$
2,000\) to be able to purchase only three cups of coffee and a donut? Assume
that the prices of coffee and donuts increase at the same rate as the CPI
during these 40 years.