How to calculate the value of LSD statistic in this case? Why is LSD useful in here?

Thomas, who is an international visiting scientist with research interests in environmental issues in urban areas, participates below in a study performed by Ville de Montreal. Thomas wants to compare the mean concentration of carbon monoxide (CO) on residential versus commercial streets, since these differ in terms of car traffic. In each of three neighborhoods of Montreal (named A, B, and C below}, he randomly chooses four locations for each type of street, for a total of 24 observations (2 street types it 3 neighborhoods x 4 locations). At each location, he measures CO concentration in the air over a period of 10 hours (3:00 AM-z00 PM), and obtains the following data (in pprnr'h). Neighborhood A B C XI." Type Residential 1.0, 1.2, 0.9, 0.5 0.4, 0.8, 0.6, 0.2 1.1, 1.4, 1.5, 1.2 0.9 1.6, 2.1, 2.5, 2.2 0.3, 1.4, 1.0, 1.2 3.0, 2.5, 3.2, 3.? 2.1 a) Draw a graph that gives insight into the possible presence of an interaction between the two classication factors. Do you suspect the presence of an interaction? Explain why