4. (10 points) The function f is continuous on the closed interval [2,8] and has values that are given in the table below. x 2 5 7 8 ns) 10 30 40 20 Using as many subintervals as possible, nd the following approximations of the area under the curve. (a) Left endpoint approximation (b) Right endpoint approximation (0) Midpoint approximation (d) Trapezoid rule