for when his son we 7 years old. Adviser made a deposit of 85 sho in the bank. The inverimont grow at a simple inerest rate and when Advisur's son was 28 years old. the value of the Invest- ment was R11 972,00 . At nhot rate the money nas invested

Let's denote the initial deposit made by the advisor as \( P \) and the interest rate as \( r \). Given: - Initial deposit, \( P = 85 \) shillings - When the advisor's son was 7 years old, the deposit was made. - When the advisor's son was 28 years old, the value of the investment was R11,972.00. We can calculate the interest rate using the formula for simple interest: \[ A = P + P \times r \times t \] where: - \( A \) is the total amount after \( t \) years - \( P \) is the initial principal amount - \( r \) is the annual interest rate - \( t \) is the time the money is invested for in years We know that when the advisor's son was 28 years old, the value of the investment was R11,972.00. This means that the total amount after 21 years (from when the deposit was made to when the son was 28 years old) was R11,972.00. Substitute the known values into the formula: \[ 11972 = 85 + 85 \times r \times 21 \] Now, we can solve for the interest rate \( r \) using the equation above. Solve the equation by following steps: - step0: Solve for \(r\): \(11972=85+85r\times 21\) - step1: Multiply the terms: \(11972=85+1785r\) - step2: Swap the sides: \(85+1785r=11972\) - step3: Move the constant to the right side: \(1785r=11972-85\) - step4: Subtract the numbers: \(1785r=11887\) - step5: Divide both sides: \(\frac{1785r}{1785}=\frac{11887}{1785}\) - step6: Divide the numbers: \(r=\frac{11887}{1785}\) The interest rate at which the money was invested is \( r = \frac{11887}{1785} \) or approximately 6.635%.