The rule of 72 states that if an investment earns $P$ % interest per year, it will take approximately $72/P$ years for your money to double.

You invest 2839 at 3.3 % interest annually.

According to the rule of 72, what is the doubling time, in years, for this investment

Use the doubling time to find a formula for $V(t)$, the value of your investment at time $t$. $V(t) =$

According to the doubling time, how much will your investment be worth after 19 years?

Use the compound interest formula to find how much the investment will be worth after 19 years. .

You may notice that your two values for the investment's worth after 19 years are different. That is because the doubling time you found with the rule of 72 is only an approximation. If the approximation were better, the two values would be the same.