A histogram represents the distribution of ages (in years) in a small town. The frequency density ($FD$) and bin widths for different age groups are provided below:

• Bin 1: Age $0-15$ years, $FD = 0.8$
• Bin 2: Age $15-25$ years, $FD = 1.5$
• Bin 3: Age $25-45$ years, $FD = 1.2$
• Bin 4: Age $45-60$ years, $FD = 0.6$

What is the total number of people in this town, based on the data presented in the histogram?