How can I go about getting the answer for both a and b

Let f(x) = 4x + 7, x1 = 2, X2 = 3, X3 = 4, x4 = 5, and Ax = 1. 4 (a) Find f (Xi) Ax. i = 1 (b) The sum in part (a) approximates a definite integral using rectangles. The height of each rectangle is given by the value of the function at the left endpoint. Write the definite integral that the sum approximates. . . . 4 (a) E f ( x; ) Ax = 1 i = 1 (Simplify your answer.) (b) Find the definite integral that is approximated by the sum in part a. 10 4 [ ( x; ) AX= ) () ax i = 1