Final answer:
It will take 7 years for the investment of R4000 at a 3% simple interest rate to earn R840.
Step-by-step explanation:
To calculate the time it will take for an investment to earn a certain amount of interest, we can use the formula:
Interest = Principal * Rate * Time
Given that the interest earned is R840, the principal is R4000, and the rate is 3%, we can substitute these values into the formula:
840 = 4000 * 0.03 * Time
Solving for Time, we get:
Time = 840 / (4000 * 0.03)
Time = 7 years
Therefore, it will take 7 years for the investment of R4000 at a 3% simple interest rate to earn R840.