According to Rule of 72, how much time will it take the prices to double at the inflation rate of 4 percent? A. Six years B. Nine years C. Twelve years D. Eighteen years

he Rule of 72 is a simple way to determine how long an investment will take to double given a fixed annual rate of interest. By dividing 72 by the annual rate of return, investors obtain a rough estimate of how many years it will take for the initial investment to duplicate itself.

So in this case you would divide 72/4 = approximately 18.5