13.68 Education and gender in modeling income Consider the relationship between yn = annual income (in thousands of dollars) and x1 = number of years of education by x2 = gender. Many studies in the United States have found that the slope for a regression equation relating y to x1 is larger for men than for women. Suppose that in the population, the regression equations are my = -10 + 4x1 for men and my = -5 + 2x1 for women. Explain why these equations imply that there is interaction between education and gender in their effects on income.