Final answer:
To find the cost of a textbook with 400 pages, substitute x = 400 into the equation. The cost would be $247.80. For a textbook with 600 pages, substitute x = 600 into the equation. The cost would be $342.20. To obtain the graph of the regression line, use a graphing calculator or software.
Step-by-step explanation:
To find the cost of a textbook with 400 pages, we can substitute the value of x into the equation. For x = 400, the equation becomes:
P = (50 + 0.4 * 400) + 0.18(50 + 0.4 * 400)
P = (50 + 160) + 0.18(50 + 160)
P = 210 + 0.18 * 210
P = 210 + 37.8 = 247.8
Therefore, the cost of a textbook with 400 pages would be $247.80.
Similarly, for a textbook with 600 pages, we can substitute x = 600 into the equation:
P = (50 + 0.4 * 600) + 0.18(50 + 0.4 * 600)
P = (50 + 240) + 0.18(50 + 240)
P = 290 + 0.18 * 290
P = 290 + 52.2 = 342.2
Therefore, the cost of a textbook with 600 pages would be $342.20.
To obtain the graph of the regression line, you can use a graphing calculator or computer software that can plot the equation and provide a visual representation of the relationship between the number of pages and the cost of the book.