The histogram shows the journey times, in minutes, of a group of commuters. The class intervals are \(0\le t\lt 10\), \(10\le t\lt 15\), \(15\le t\lt 20\), \(20\le t\lt 30\) and \(30\le t\lt 50\), so the bars have unequal widths and the vertical axis shows frequency density.



Assuming the journey times are spread evenly within each class, estimate the number of commuters whose journey time \(t\) satisfies \(12\le t\lt 36\).