Refer to exhibit 15-6. the interpretation of the coefficient of x1 is that a. a one unit increase in x1 will lead to a 3.682 unit decrease in y when all other variables are held constant b. a one unit increase in x1 will lead to a 3.682 unit decrease in x2 when all other variables are held constant c. it is impossible to interpret the coefficient. d. a one unit change in x1 will lead to a 3.682 unit decrease in y