(a) Estimate the area under the graph of $f(x) = 3 + x^2$ from $x = -1$ to $x = 2$ using three approximating rectangles and right endpoints.

$R_3 =$

(b) Repeat part (a) using six approximating rectangles and right endpoints.

$R_6 =$

(c) Repeat part (a) using three approximating rectangles and left endpoints.

$L_3 =$

(d) Repeat part (a) using six approximating rectangles and left endpoints.

$L_6 =$

(e) Repeat part (a) using three approximating rectangles and midpoints.

$M_3 =$

(f) Repeat part (a) using six approximating rectangles and midpoints.

$M_6 =$

Based on sketches of the graph of $f(x)$ and the approximating rectangles, which appears to be the best estimate?

A. $R_6$
B. $L_3$
C. $M_6$
D. $L_6$
E. $M_3$
F. $R_3$