A survey of young people's shopping habits in a small city during the summer months of 2009 showed the following: Shoppers aged 12 to 14 years took an average of 10 shopping trips per month and spent an average of $15 per trip. Shoppers aged 15 to 17 years took an average of 11 trips per month and spent an average of $17 per trip. Assume that this city has 1100 shoppers aged 12 to 14 years and 900 shoppers aged 15 to 17 years.
Find the mean amount spent per person per month by shoppers aged 12 to 17 years in this city.