(i) Plot the cumulative frequency points: (40, 0), (50, 12), (60, 34), (65, 64), (70, 92), (90, 144). Draw a smooth curve through these points.

(ii) To find \(c\), note that 64 people weigh more than \(c\), so 80 people weigh less than \(c\). From the graph, this corresponds to a weight of 67.2 kg. Thus, \(c = 67.2\) kg.

(iii) Calculate the frequencies: 12, 22, 30, 28, 52. Use midpoints: 45, 55, 62.5, 67.5, 80. Calculate the mean:

\(\text{Mean} = \frac{(45 \times 12) + (55 \times 22) + (62.5 \times 30) + (67.5 \times 28) + (80 \times 52)}{144} = \frac{9675}{144} = 67.2 \text{ kg}\)

\(Calculate the variance:\)

\(\text{Variance} = \frac{(45^2 \times 12) + (55^2 \times 22) + (62.5^2 \times 30) + (67.5^2 \times 28) + (80^2 \times 52)}{144} - (67.2)^2 = 127.59\)

Standard deviation:

\(\text{Standard deviation} = \sqrt{127.59} = 11.3 \text{ kg}\)