(i) To draw the cumulative frequency graph, calculate the cumulative frequencies:

• 3 – 5 seconds: Cumulative frequency = 10
• 6 – 8 seconds: Cumulative frequency = 10 + 15 = 25
• 9 – 11 seconds: Cumulative frequency = 25 + 17 = 42
• 12 – 16 seconds: Cumulative frequency = 42 + 4 = 46
• 17 – 25 seconds: Cumulative frequency = 46 + 2 = 48

Plot these cumulative frequencies against the upper class boundaries: (5.5, 10), (8.5, 25), (11.5, 42), (16.5, 46), (25.5, 48).

(ii) To find \(t\), note that 35 cars accelerated in more than \(t\) seconds, so 13 cars accelerated in \(t\) seconds or less. From the cumulative frequency graph, find the time corresponding to a cumulative frequency of 13. This gives \(t \approx 6.5\) seconds, so \(6 < t < 7\).