Approximate the area under the following curve and above the x-axis on the given interval, using rectangles whose height is the value of the function at the left side of the rectangle. (a) Use two rectangles. (b) Use four rectangles. f(x) = 4+x; [-1,1] (a) The approximated area when using two rectangles is square units. (Type an integer or decimal rounded to two decimal places as needed.) (b) The approximated area when using four rectangles is square units. (Type an integer or decimal rounded to two decimal places as needed.)