Data was collected for 309 randomly selected 10 minute intervals. For each ten-minute interval, the number of people entering the atrium of a large mall were recorded. The data is summarized in the table below.

Number
of Guests Frequency
120 – 124 55
125 – 129 74
130 – 134 90
135 – 139 41
140 – 144 49


What is the class width for this Frequency Distribution Table?