Consider the region below f(x) = (6 - x), above the xaxis, and between X: 0 and x = 6. Let Xi be the midpoint of the ith subinterval. Complete parts a. and b. below. (... 3. Approximate the area of the region using six rectangles. Use the midpoints of each subinterval for the heights of the rectangles. The area is approximately :I square units. (Type an integer or decimal.) 6 b. Find {(6 - x) dx by using the formula for the area of a triangle. 0 6 {(6 - x) dx = D (Simplify your answer.) 0