John wants to determine if adult residents in Eastgate, Ohio are in favor of the new traffic circles that have been implemented in the area. He decides to conduct a sample survey in order to determine this. He secures a list of all the residents of the Eastgate area. He sorts them into groups by age: young (18-34), middle-aged (35-54), and older (55 and older). He randomly selects 25 young residents, 25 middle-aged residents, and 25 older residents to send the survey to. What kind of sample is this