The length of time required for the investment to triple its value if the annual rate of return remains the same is 16.23 years assuming the investor gets a compounded return. If the investor gets a simple return then the length of time required for the investment to triple its value is 28.57 years. The length with a compounded interest calculation: 16.23 = log (1+7%) (6000/2000). The length with a simple interest calculation: 28.57 = (6000-2000)/(2000*7%).