13.41 Park Jeong-Hoon owns a bread store in Itaewon, South Korea. He believes that the number of hot dog buns ordered by customers that visit his store has an interaction effect on the combination of the three different types of condiment (mayonnaise, ketchup, and mustard) with the topping of salsa. Therefore, he determines the following regression model:

Y = b0 + b1X1 + b2X2 + b3X3 + 1b4X1 + b5X22X3

= b0 + b1X1 + b2X2 + b3X3 + b4X1X3 + b5X2X3 where Y = order X1 = mayonnaise X2 = ketchup X3 = salsa From a random sample, Jeong-Hoon estimated the constant and the slope coefficients as b0 = 3.5, b1 = 1.347, b2 = 0.428, b3 = 3.475, b4 = 0.709, and b5 = -1.0396.

Help Jeong-Hoon interpret the estimated slope coefficient values, b1, b2, b3, and 1b3 + b42.