The bar graph shows the median annual income for residents of a selected region of the United
States, by level of education. The given polynomial models describe the median annual income
for men, M, and for women, W, who have completed x years of education.
M = – 23x3+ 1170x2– 13,808x + 72,566
W = 8x3– 56x2+ 511x + 14,763
Find a mathematical model for M – W and use it to calculate the difference in the median annual
income between men and women with 8 years of education. Does the model underestimate or
overestimate the actual difference?