Answer:
It will take an interest rate of 8.1% to get 150% of the initial investment in just 5 years.
Step-by-step explanation:
Use the formula for continuous compounding
where r stands for the (annual) interest rate, t for time in years, P for the initial principal (investment) and X is the amount after t years.
(this formula can be beautifully derived from just basic considerations, btw)
We are given t=5, and percent increase on the initial P, so we can solve for r
It will take an interest rate of 8.1% to get 150% of the initial investment in just 5 years.