7.3 HW Q5 I don't understand my Homwork

Approximate the area under the graph of f(x) and above the x-axis with rectangles, using the following methods with n = 4. f(x) = 8x + 4 from x = 5 to x = 7 a. Use left endpoints. b. Use right endpoints. c. Average the answers in parts a and b. d. Use midpoints. . . . a. The area, approximated using the left endpoints, is