please answer the 3 questions

E Open with Google Docs THINKING (14 marks) 19. Use the first or second derivative test (or both) to find the local maximum or minimum points of f(x) = x - 8x + 18x . (4 marks)0 3 are both LOCAL MAX 20. A box with an open top is constructed from a rectangular piece of cardboard 2m x 3m by cutting a square from each of the four corners and bending up the sides. Determine the the dimensions of the box if it is to have a maximum volume. (6 marks) X V = 1wh1 21. Determine the points of inflection of X +3