(i) To find the mean age of all 24 cars, we calculate the total sum of ages and divide by the total number of cars:

For Red Street Garage: \(\text{Total sum} = 3.6 \times 9 = 32.4\)

For Fairwheel Garage: \(\Sigma x = 64\)

Total sum of ages = \(32.4 + 64 = 96.4\)

\(Total number of cars = 9 + 15 = 24\)

Mean age = \(\frac{96.4}{24} = 4.02 \text{ years}\)

\((ii) To find the standard deviation of all 24 cars, we first find the variance:\)

Variance for Red Street Garage: \(\frac{\Sigma x^2}{9} - 3.6^2 = 1.925^2\)

\(\Sigma x^2 = 150\)

Total \(\Sigma x^2 = 150 + 352 = 502\)

\(Mean age = 4.02\)

Variance = \(\frac{502}{24} - 4.02^2 = 4.780\)

Standard deviation = \(\sqrt{4.780} = 2.19 \text{ years}\)