=+5.25 ● Representative data on x 5 carbonation depth (in millimeters) and y 5 strength (in megapascals) for a sample of concrete core specimens taken from a particular building were read from a plot in the article “The Carbonation of Concrete Structures in the Tropical Environment of Singapore” (Magazine of Concrete Research [1996]: 293–300):

Depth, x 8.0 20.0 20.0 30.0 35.0 Strength, y 22.8 17.1 21.1 16.1 13.4 Depth, x 40.0 50.0 55.0 65.0 Strength, y 12.4 11.4 9.7 6.8