Approximate the area A of the region enclosed by the graph of f (x) = 10 - 2x, the x-axis, and the lines x = 2 and x = 4 by partitioning the closed interval [2, 4] into four subintervals. (Give exact answers. Use symbolic notation and fractions where needed.) Use the right endpoint of each subinterval. A = Use the left endpoint of each subinterval. A =