What property is being used for 8x-2+x-14 and 9(4m+1) and lastly 3(-2x+7) i already know the answers for those, i just need with the question that says "what property is being used for those problems"

Aresearch study is done to find the average age of all u. s. factory workers. the researchers asked every factory worker in ohio what their birth year is. this research is an example of a census survey convenience sample simple random sample