Answer:
It takes 75 years for the investment to quadruple in value
Explanation:
Simple Interest
This is a simple interest problem.
The simple interest formula is given by:

In which E is the amount of interest earned, P is the principal(the initial amount of money), I is the interest rate(yearly, as a decimal) and t is the time.
After t years, the total amount of money is:

In this question:
4% simple interest per year, so I = 0.04.
Quadruple:
t when T = 4P.
The interest earned is:



Now we find the time.





It takes 75 years for the investment to quadruple in value